feat(pdfengines): redesign Factur-X API with dedicated form fields

.bruno/Chromium/Convert/HTML to PDF.bru

@@ -53,7 +53,10 @@ body:multipart-form {
   ~embeds: @file(../test/integration/testdata/embed_1.xml)
   ~embeds: @file(../test/integration/testdata/embed_2.xml)
   ~embedsMetadata: {"embed_1.xml":{"mimeType":"text/xml","relationship":"Data"}, "embed_2.xml":{"mimeType":"text/xml","relationship":"Data"}}
-  ~facturx: {"conformanceLevel":"EN 16931","documentType":"INVOICE","documentFileName":"factur-x.xml","version":"1.0"}
+  ~facturxXml: @file(../test/integration/testdata/embed_1.xml)
+  ~facturxConformanceLevel: EN 16931
+  ~facturxDocumentType: INVOICE
+  ~facturxVersion: 1.0
   ~watermarkSource: text
   ~watermarkExpression: CONFIDENTIAL
   ~watermarkPages:

.bruno/Chromium/Convert/Markdown to PDF.bru

@@ -54,7 +54,10 @@ body:multipart-form {
   ~embeds: @file(../test/integration/testdata/embed_1.xml)
   ~embeds: @file(../test/integration/testdata/embed_2.xml)
   ~embedsMetadata: {"embed_1.xml":{"mimeType":"text/xml","relationship":"Data"}, "embed_2.xml":{"mimeType":"text/xml","relationship":"Data"}}
-  ~facturx: {"conformanceLevel":"EN 16931","documentType":"INVOICE","documentFileName":"factur-x.xml","version":"1.0"}
+  ~facturxXml: @file(../../test/integration/testdata/embed_1.xml)
+  ~facturxConformanceLevel: EN 16931
+  ~facturxDocumentType: INVOICE
+  ~facturxVersion: 1.0
   ~watermarkSource: text
   ~watermarkExpression: CONFIDENTIAL
   ~watermarkPages:

.bruno/Chromium/Convert/URL to PDF.bru

@@ -53,7 +53,10 @@ body:multipart-form {
   ~embeds: @file(../test/integration/testdata/embed_1.xml)
   ~embeds: @file(../test/integration/testdata/embed_2.xml)
   ~embedsMetadata: {"embed_1.xml":{"mimeType":"text/xml","relationship":"Data"}, "embed_2.xml":{"mimeType":"text/xml","relationship":"Data"}}
-  ~facturx: {"conformanceLevel":"EN 16931","documentType":"INVOICE","documentFileName":"factur-x.xml","version":"1.0"}
+  ~facturxXml: @file(../test/integration/testdata/embed_1.xml)
+  ~facturxConformanceLevel: EN 16931
+  ~facturxDocumentType: INVOICE
+  ~facturxVersion: 1.0
   ~watermarkSource: text
   ~watermarkExpression: CONFIDENTIAL
   ~watermarkPages:

.bruno/LibreOffice/Convert to PDF.bru

@@ -70,7 +70,10 @@ body:multipart-form {
   ~embeds: @file(../test/integration/testdata/embed_1.xml)
   ~embeds: @file(../test/integration/testdata/embed_2.xml)
   ~embedsMetadata: {"embed_1.xml":{"mimeType":"text/xml","relationship":"Data"}, "embed_2.xml":{"mimeType":"text/xml","relationship":"Data"}}
-  ~facturx: {"conformanceLevel":"EN 16931","documentType":"INVOICE","documentFileName":"factur-x.xml","version":"1.0"}
+  ~facturxXml: @file(../test/integration/testdata/embed_1.xml)
+  ~facturxConformanceLevel: EN 16931
+  ~facturxDocumentType: INVOICE
+  ~facturxVersion: 1.0
   ~watermarkSource: text
   ~watermarkExpression: CONFIDENTIAL
   ~watermarkPages:

.bruno/PDF Engines/Embed/Embed Files.bru

@@ -15,7 +15,10 @@ body:multipart-form {
   embeds: @file(../test/integration/testdata/embed_1.xml)
   embeds: @file(../test/integration/testdata/embed_2.xml)
   embedsMetadata: {"embed_1.xml":{"mimeType":"text/xml","relationship":"Data"}, "embed_2.xml":{"mimeType":"text/xml","relationship":"Data"}}
-  ~facturx: {"conformanceLevel":"EN 16931","documentType":"INVOICE","documentFileName":"factur-x.xml","version":"1.0"}
+  ~facturxXml: @file(../test/integration/testdata/embed_1.xml)
+  ~facturxConformanceLevel: EN 16931
+  ~facturxDocumentType: INVOICE
+  ~facturxVersion: 1.0
   ~downloadFrom: [{"url":"https://example.com/attachment.xml","embedded":true}]
 }
 

.bruno/PDF Engines/Factur-X/Inject Factur-X XMP.bru

@@ -12,7 +12,10 @@ post {
 
 body:multipart-form {
   files: @file(../../test/integration/testdata/page_1.pdf)
-  facturx: {"conformanceLevel":"EN 16931","documentType":"INVOICE","documentFileName":"factur-x.xml","version":"1.0"}
+  facturxXml: @file(../../test/integration/testdata/embed_1.xml)
+  facturxConformanceLevel: EN 16931
+  ~facturxDocumentType: INVOICE
+  ~facturxVersion: 1.0
 }
 
 headers {

.bruno/PDF Engines/Merge/Merge PDFs.bru

@@ -31,7 +31,10 @@ body:multipart-form {
   ~stampOptions: {"scale":"0.5 abs","rot":"45"}
   ~rotateAngle: 90
   ~rotatePages:
-  ~facturx: {"conformanceLevel":"EN 16931","documentType":"INVOICE","documentFileName":"factur-x.xml","version":"1.0"}
+  ~facturxXml: @file(../../test/integration/testdata/embed_1.xml)
+  ~facturxConformanceLevel: EN 16931
+  ~facturxDocumentType: INVOICE
+  ~facturxVersion: 1.0
 }
 
 headers {

.bruno/PDF Engines/Split/Split PDF.bru

@@ -31,7 +31,10 @@ body:multipart-form {
   ~stampOptions: {"scale":"0.5 abs","rot":"45"}
   ~rotateAngle: 90
   ~rotatePages:
-  ~facturx: {"conformanceLevel":"EN 16931","documentType":"INVOICE","documentFileName":"factur-x.xml","version":"1.0"}
+  ~facturxXml: @file(../../test/integration/testdata/embed_1.xml)
+  ~facturxConformanceLevel: EN 16931
+  ~facturxDocumentType: INVOICE
+  ~facturxVersion: 1.0
 }
 
 headers {

pkg/gotenberg/mocks.go

@@ -45,22 +45,23 @@ func (mod *DebuggableMock) Debug() map[string]any {
 //
 //nolint:dupl
 type PdfEngineMock struct {
-	MergeMock              func(ctx context.Context, logger *slog.Logger, inputPaths []string, outputPath string) error
-	SplitMock              func(ctx context.Context, logger *slog.Logger, mode SplitMode, inputPath, outputDirPath string) ([]string, error)
-	FlattenMock            func(ctx context.Context, logger *slog.Logger, inputPath string) error
-	ConvertMock            func(ctx context.Context, logger *slog.Logger, formats PdfFormats, inputPath, outputPath string) error
-	ReadMetadataMock       func(ctx context.Context, logger *slog.Logger, inputPath string) (map[string]any, error)
-	PageCountMock          func(ctx context.Context, logger *slog.Logger, inputPath string) (int, error)
-	WriteMetadataMock      func(ctx context.Context, logger *slog.Logger, metadata map[string]any, inputPath string) error
-	ReadBookmarksMock      func(ctx context.Context, logger *slog.Logger, inputPath string) ([]Bookmark, error)
-	EncryptMock            func(ctx context.Context, logger *slog.Logger, inputPath, userPassword, ownerPassword string) error
-	EmbedFilesMock         func(ctx context.Context, logger *slog.Logger, filePaths []string, inputPath string) error
-	EmbedFilesMetadataMock func(ctx context.Context, logger *slog.Logger, metadata map[string]map[string]string, inputPath string) error
-	WriteBookmarksMock     func(ctx context.Context, logger *slog.Logger, inputPath string, bookmarks []Bookmark) error
-	WatermarkMock          func(ctx context.Context, logger *slog.Logger, inputPath string, stamp Stamp) error
-	StampMock              func(ctx context.Context, logger *slog.Logger, inputPath string, stamp Stamp) error
-	RotateMock             func(ctx context.Context, logger *slog.Logger, inputPath string, angle int, pages string) error
-	InjectFacturXXMPMock   func(ctx context.Context, logger *slog.Logger, facturX FacturX, inputPath string) error
+	MergeMock               func(ctx context.Context, logger *slog.Logger, inputPaths []string, outputPath string) error
+	SplitMock               func(ctx context.Context, logger *slog.Logger, mode SplitMode, inputPath, outputDirPath string) ([]string, error)
+	FlattenMock             func(ctx context.Context, logger *slog.Logger, inputPath string) error
+	ConvertMock             func(ctx context.Context, logger *slog.Logger, formats PdfFormats, inputPath, outputPath string) error
+	ReadMetadataMock        func(ctx context.Context, logger *slog.Logger, inputPath string) (map[string]any, error)
+	PageCountMock           func(ctx context.Context, logger *slog.Logger, inputPath string) (int, error)
+	WriteMetadataMock       func(ctx context.Context, logger *slog.Logger, metadata map[string]any, inputPath string) error
+	ReadBookmarksMock       func(ctx context.Context, logger *slog.Logger, inputPath string) ([]Bookmark, error)
+	EncryptMock             func(ctx context.Context, logger *slog.Logger, inputPath, userPassword, ownerPassword string) error
+	EmbedFilesMock          func(ctx context.Context, logger *slog.Logger, filePaths []string, inputPath string) error
+	EmbedFilesMetadataMock  func(ctx context.Context, logger *slog.Logger, metadata map[string]map[string]string, inputPath string) error
+	WriteBookmarksMock      func(ctx context.Context, logger *slog.Logger, inputPath string, bookmarks []Bookmark) error
+	WatermarkMock           func(ctx context.Context, logger *slog.Logger, inputPath string, stamp Stamp) error
+	StampMock               func(ctx context.Context, logger *slog.Logger, inputPath string, stamp Stamp) error
+	RotateMock              func(ctx context.Context, logger *slog.Logger, inputPath string, angle int, pages string) error
+	InjectFacturXXMPMock    func(ctx context.Context, logger *slog.Logger, facturX FacturX, inputPath string) error
+	ReadPdfAConformanceMock func(ctx context.Context, logger *slog.Logger, inputPath string) (string, string, error)
 }
 
 func (engine *PdfEngineMock) Merge(ctx context.Context, logger *slog.Logger, inputPaths []string, outputPath string) error {
@@ -127,6 +128,10 @@ func (engine *PdfEngineMock) InjectFacturXXMP(ctx context.Context, logger *slog.
 	return engine.InjectFacturXXMPMock(ctx, logger, facturX, inputPath)
 }
 
+func (engine *PdfEngineMock) ReadPdfAConformance(ctx context.Context, logger *slog.Logger, inputPath string) (string, string, error) {
+	return engine.ReadPdfAConformanceMock(ctx, logger, inputPath)
+}
+
 // PdfEngineProviderMock is a mock for the [PdfEngineProvider] interface.
 type PdfEngineProviderMock struct {
 	PdfEngineMock func() (PdfEngine, error)

pkg/gotenberg/pdfengine.go

@@ -185,6 +185,10 @@ const (
 
 	// FacturXDocumentTypeOrderChange represents the ORDER_CHANGE Factur-X document type.
 	FacturXDocumentTypeOrderChange string = "ORDER_CHANGE"
+
+	// FacturXDocumentFileName is the canonical name of the embedded XML invoice
+	// mandated by the Factur-X standard. Validators expect this exact name.
+	FacturXDocumentFileName string = "factur-x.xml"
 )
 
 // FacturX gathers the properties required by the Factur-X/ZUGFeRD standard for
@@ -196,8 +200,8 @@ type FacturX struct {
 	// DocumentType is one of the FacturXDocumentType* values.
 	DocumentType string
 
-	// DocumentFileName is the name of the embedded XML invoice (e.g.,
-	// "factur-x.xml").
+	// DocumentFileName is the name of the embedded XML invoice. It is set
+	// internally to the canonical [FacturXDocumentFileName], not by the caller.
 	DocumentFileName string
 
 	// Version is the Factur-X version (e.g., "1.0").
@@ -275,6 +279,12 @@ type PdfEngine interface {
 	// registers the fx namespace, the four fx properties, and the matching
 	// PDF/A extension schema so the result stays PDF/A-valid.
 	InjectFacturXXMP(ctx context.Context, logger *slog.Logger, facturX FacturX, inputPath string) error
+
+	// ReadPdfAConformance reads the PDF/A part and conformance (e.g., "3" and
+	// "B") from the document-level XMP packet (Catalog /Metadata stream,
+	// pdfaid:part and pdfaid:conformance). It returns empty strings when the
+	// document carries no PDF/A identification.
+	ReadPdfAConformance(ctx context.Context, logger *slog.Logger, inputPath string) (part string, conformance string, err error)
 }
 
 // PdfEngineProvider offers an interface to instantiate a [PdfEngine].

pkg/modules/api/formdata.go

@@ -26,6 +26,10 @@ const (
 
 	// StampFormField represents the form field name for the stamp file.
 	StampFormField string = "stamp"
+
+	// FacturXXmlFormField represents the form field name for the Factur-X CII
+	// invoice XML file.
+	FacturXXmlFormField string = "facturxXml"
 )
 
 // FormData is a helper for validating and hydrating values from a
@@ -424,89 +428,6 @@ func (form *FormData) EmbedsMetadata(target *map[string]map[string]string) *Form
 	return form
 }
 
-// FacturX parses the "facturx" form field (a JSON string) into a
-// [gotenberg.FacturX]. The "conformanceLevel" property is mandatory; the
-// "documentType", "version", and "documentFileName" properties default to
-// "INVOICE", "1.0", and "factur-x.xml" respectively. It leaves the target
-// untouched when the field is absent.
-//
-//	var facturX gotenberg.FacturX
-//
-//	ctx.FormData().FacturX(&facturX, false)
-func (form *FormData) FacturX(target *gotenberg.FacturX, mandatory bool) *FormData {
-	if form.errors != nil {
-		return form
-	}
-
-	val, ok := form.values["facturx"]
-	if !ok || len(val) == 0 || val[0] == "" {
-		if mandatory {
-			form.append(fmt.Errorf("form field '%s' is required", "facturx"))
-		}
-		return form
-	}
-
-	var parsed struct {
-		ConformanceLevel string `json:"conformanceLevel"`
-		DocumentType     string `json:"documentType"`
-		DocumentFileName string `json:"documentFileName"`
-		Version          string `json:"version"`
-	}
-
-	err := json.Unmarshal([]byte(val[0]), &parsed)
-	if err != nil {
-		form.append(fmt.Errorf("form field 'facturx' is invalid: %w", err))
-		return form
-	}
-
-	facturX := gotenberg.FacturX{
-		ConformanceLevel: parsed.ConformanceLevel,
-		DocumentType:     parsed.DocumentType,
-		DocumentFileName: parsed.DocumentFileName,
-		Version:          parsed.Version,
-	}
-
-	if facturX.DocumentType == "" {
-		facturX.DocumentType = gotenberg.FacturXDocumentTypeInvoice
-	}
-
-	if facturX.Version == "" {
-		facturX.Version = "1.0"
-	}
-
-	if facturX.DocumentFileName == "" {
-		facturX.DocumentFileName = "factur-x.xml"
-	}
-
-	switch facturX.ConformanceLevel {
-	case gotenberg.FacturXConformanceMinimum,
-		gotenberg.FacturXConformanceBasicWL,
-		gotenberg.FacturXConformanceBasic,
-		gotenberg.FacturXConformanceEN16931,
-		gotenberg.FacturXConformanceExtended,
-		gotenberg.FacturXConformanceXRechnung:
-	case "":
-		form.append(errors.New("form field 'facturx' is invalid: 'conformanceLevel' is required"))
-		return form
-	default:
-		form.append(fmt.Errorf("form field 'facturx' is invalid: unsupported 'conformanceLevel' '%s'", facturX.ConformanceLevel))
-		return form
-	}
-
-	switch facturX.DocumentType {
-	case gotenberg.FacturXDocumentTypeInvoice,
-		gotenberg.FacturXDocumentTypeOrder,
-		gotenberg.FacturXDocumentTypeOrderResponse,
-		gotenberg.FacturXDocumentTypeOrderChange:
-	default:
-		form.append(fmt.Errorf("form field 'facturx' is invalid: unsupported 'documentType' '%s'", facturX.DocumentType))
-		return form
-	}
-
-	*target = facturX
-	return form
-}
-
 // MandatoryPaths binds the absolute paths of form data files, according to a
 // list of file extensions, to a string slice variable. It populates an error
 // if there is no file for given file extensions.
@@ -558,13 +479,28 @@ func (form *FormData) Stamp(target *string) *FormData {
 	return form
 }
 
+// FacturXXml binds the absolute path of the uploaded Factur-X CII invoice
+// XML. Only a file uploaded with the "facturxXml" field name is included.
+func (form *FormData) FacturXXml(target *string) *FormData {
+	if form.errors != nil {
+		return form
+	}
+
+	if paths, ok := form.filesByField[FacturXXmlFormField]; ok && len(paths) > 0 {
+		*target = paths[0]
+	}
+
+	return form
+}
+
 // paths bind the absolute paths of form data files, according to a list of
 // file extensions, to a string slice variable.
-// embeds, watermark, and stamp files are excluded.
+// embeds, watermark, stamp, and facturxXml files are excluded.
 func (form *FormData) paths(extensions []string, target *[]string) *FormData {
 	embeds, ok := form.filesByField[EmbedsFormField]
 	watermarks, wmOk := form.filesByField[WatermarkFormField]
 	stamps, stOk := form.filesByField[StampFormField]
+	facturxXmls, fxOk := form.filesByField[FacturXXmlFormField]
 
 	// Collect (originalFilename, diskPath) pairs so that we can sort by
 	// original filename rather than by UUID-based disk name.
@@ -588,6 +524,10 @@ func (form *FormData) paths(extensions []string, target *[]string) *FormData {
 			continue
 		}
 
+		if fxOk && slices.Contains(facturxXmls, path) {
+			continue
+		}
+
 		for _, ext := range extensions {
 			// See https://github.com/gotenberg/gotenberg/issues/228.
 			if strings.ToLower(filepath.Ext(filename)) == ext {

pkg/modules/api/formdata_test.go

@@ -7,8 +7,6 @@ import (
 	"reflect"
 	"testing"
 	"time"
-
-	"github.com/gotenberg/gotenberg/v8/pkg/gotenberg"
 )
 
 func TestFormData_Validate(t *testing.T) {
@@ -1786,110 +1784,56 @@ func TestFormData_Embeds(t *testing.T) {
 	}
 }
 
-func TestFormData_FacturX(t *testing.T) {
+func TestFormData_FacturXXml(t *testing.T) {
 	for _, tc := range []struct {
-		scenario  string
-		form      *FormData
-		mandatory bool
-		expect    gotenberg.FacturX
-		expectErr bool
+		scenario string
+		form     *FormData
+		expect   string
 	}{
 		{
-			scenario:  "key does not exist, not mandatory",
-			form:      &FormData{},
-			mandatory: false,
-			expect:    gotenberg.FacturX{},
+			scenario: "no facturxXml file",
+			form:     &FormData{},
+			expect:   "",
 		},
 		{
-			scenario:  "key does not exist, mandatory",
-			form:      &FormData{},
-			mandatory: true,
-			expectErr: true,
-		},
-		{
-			scenario: "all fields provided",
+			scenario: "facturxXml file present",
 			form: &FormData{
-				values: map[string][]string{
-					"facturx": {`{"conformanceLevel":"EXTENDED","documentType":"ORDER","documentFileName":"order.xml","version":"2.0"}`},
+				filesByField: map[string][]string{
+					FacturXXmlFormField: {"/tmp/abc/12345.xml"},
 				},
 			},
-			expect: gotenberg.FacturX{
-				ConformanceLevel: gotenberg.FacturXConformanceExtended,
-				DocumentType:     gotenberg.FacturXDocumentTypeOrder,
-				DocumentFileName: "order.xml",
-				Version:          "2.0",
-			},
-		},
-		{
-			scenario: "only conformance level, defaults applied",
-			form: &FormData{
-				values: map[string][]string{
-					"facturx": {`{"conformanceLevel":"EN 16931"}`},
-				},
-			},
-			expect: gotenberg.FacturX{
-				ConformanceLevel: gotenberg.FacturXConformanceEN16931,
-				DocumentType:     gotenberg.FacturXDocumentTypeInvoice,
-				DocumentFileName: "factur-x.xml",
-				Version:          "1.0",
-			},
-		},
-		{
-			scenario: "invalid JSON",
-			form: &FormData{
-				values: map[string][]string{
-					"facturx": {`{not json`},
-				},
-			},
-			expectErr: true,
-		},
-		{
-			scenario: "missing conformance level",
-			form: &FormData{
-				values: map[string][]string{
-					"facturx": {`{"documentType":"INVOICE"}`},
-				},
-			},
-			expectErr: true,
-		},
-		{
-			scenario: "unsupported conformance level",
-			form: &FormData{
-				values: map[string][]string{
-					"facturx": {`{"conformanceLevel":"FOO"}`},
-				},
-			},
-			expectErr: true,
-		},
-		{
-			scenario: "unsupported document type",
-			form: &FormData{
-				values: map[string][]string{
-					"facturx": {`{"conformanceLevel":"BASIC","documentType":"RECEIPT"}`},
-				},
-			},
-			expectErr: true,
+			expect: "/tmp/abc/12345.xml",
 		},
 	} {
 		t.Run(tc.scenario, func(t *testing.T) {
-			var actual gotenberg.FacturX
+			var actual string
 
-			tc.form.FacturX(&actual, tc.mandatory)
+			tc.form.FacturXXml(&actual)
 
-			if tc.expectErr {
-				if tc.form.errors == nil {
-					t.Error("expected an error but got none")
-				}
-				return
-			}
-
-			if tc.form.errors != nil {
-				t.Errorf("expected no error but got: %v", tc.form.errors)
-			}
-
-			if !reflect.DeepEqual(actual, tc.expect) {
-				t.Errorf("expected %+v but got %+v", tc.expect, actual)
+			if actual != tc.expect {
+				t.Errorf("expected %q but got %q", tc.expect, actual)
 			}
 		})
 	}
 }
+
+// TestFormData_paths_excludesFacturXXml verifies that an uploaded facturxXml is
+// never picked up as an input document by paths().
+func TestFormData_paths_excludesFacturXXml(t *testing.T) {
+	form := &FormData{
+		files: map[string]string{
+			"document.xml": "/tmp/abc/document.xml",
+			"factur-x.xml": "/tmp/abc/invoice.xml",
+		},
+		filesByField: map[string][]string{
+			FacturXXmlFormField: {"/tmp/abc/invoice.xml"},
+		},
+	}
+
+	var paths []string
+	form.paths([]string{".xml"}, &paths)
+
+	if len(paths) != 1 || paths[0] != "/tmp/abc/document.xml" {
+		t.Errorf("expected only the non-Factur-X .xml document, got %+v", paths)
+	}
+}

pkg/modules/chromium/routes.go

@@ -454,7 +454,7 @@ func convertUrlRoute(chromium Api, engine gotenberg.PdfEngine) api.Route {
 			stampFile := pdfengines.FormDataPdfStampFile(form)
 			rotateAngle, rotatePages := pdfengines.FormDataPdfRotate(form, false)
 			embedsMetadata := pdfengines.FormDataPdfEmbedsMetadata(form)
-			facturX := pdfengines.FormDataPdfFacturX(form, false)
+			facturX, facturxXmlPath := pdfengines.FormDataPdfFacturX(form)
 
 			var url string
 			err := form.
@@ -478,7 +478,7 @@ func convertUrlRoute(chromium Api, engine gotenberg.PdfEngine) api.Route {
 				return fmt.Errorf("validate stamp: %w", err)
 			}
 
-			err = convertUrl(ctx, chromium, engine, url, options, mode, pdfFormats, metadata, userPassword, ownerPassword, embedPaths, embedsMetadata, facturX, watermark, stamp, rotateAngle, rotatePages)
+			err = convertUrl(ctx, chromium, engine, url, options, mode, pdfFormats, metadata, userPassword, ownerPassword, embedPaths, embedsMetadata, facturX, facturxXmlPath, watermark, stamp, rotateAngle, rotatePages)
 			if err != nil {
 				return fmt.Errorf("convert URL to PDF: %w", err)
 			}
@@ -543,7 +543,7 @@ func convertHtmlRoute(chromium Api, engine gotenberg.PdfEngine) api.Route {
 			stampFile := pdfengines.FormDataPdfStampFile(form)
 			rotateAngle, rotatePages := pdfengines.FormDataPdfRotate(form, false)
 			embedsMetadata := pdfengines.FormDataPdfEmbedsMetadata(form)
-			facturX := pdfengines.FormDataPdfFacturX(form, false)
+			facturX, facturxXmlPath := pdfengines.FormDataPdfFacturX(form)
 
 			var inputPath string
 			err := form.
@@ -564,7 +564,7 @@ func convertHtmlRoute(chromium Api, engine gotenberg.PdfEngine) api.Route {
 
 			url := fmt.Sprintf("file://%s", inputPath)
 			options.AllowedFilePrefixes = []string{ctx.DirPath()}
-			err = convertUrl(ctx, chromium, engine, url, options, mode, pdfFormats, metadata, userPassword, ownerPassword, embedPaths, embedsMetadata, facturX, watermark, stamp, rotateAngle, rotatePages)
+			err = convertUrl(ctx, chromium, engine, url, options, mode, pdfFormats, metadata, userPassword, ownerPassword, embedPaths, embedsMetadata, facturX, facturxXmlPath, watermark, stamp, rotateAngle, rotatePages)
 			if err != nil {
 				return fmt.Errorf("convert HTML to PDF: %w", err)
 			}
@@ -626,7 +626,7 @@ func convertMarkdownRoute(chromium Api, engine gotenberg.PdfEngine) api.Route {
 			stampFile := pdfengines.FormDataPdfStampFile(form)
 			rotateAngle, rotatePages := pdfengines.FormDataPdfRotate(form, false)
 			embedsMetadata := pdfengines.FormDataPdfEmbedsMetadata(form)
-			facturX := pdfengines.FormDataPdfFacturX(form, false)
+			facturX, facturxXmlPath := pdfengines.FormDataPdfFacturX(form)
 
 			var (
 				inputPath     string
@@ -656,7 +656,7 @@ func convertMarkdownRoute(chromium Api, engine gotenberg.PdfEngine) api.Route {
 			}
 
 			options.AllowedFilePrefixes = []string{ctx.DirPath()}
-			err = convertUrl(ctx, chromium, engine, url, options, mode, pdfFormats, metadata, userPassword, ownerPassword, embedPaths, embedsMetadata, facturX, watermark, stamp, rotateAngle, rotatePages)
+			err = convertUrl(ctx, chromium, engine, url, options, mode, pdfFormats, metadata, userPassword, ownerPassword, embedPaths, embedsMetadata, facturX, facturxXmlPath, watermark, stamp, rotateAngle, rotatePages)
 			if err != nil {
 				return fmt.Errorf("convert markdown to PDF: %w", err)
 			}
@@ -781,7 +781,7 @@ func markdownToHtml(ctx *api.Context, inputPath string, markdownPaths []string)
 	return fmt.Sprintf("file://%s", inputPath), nil
 }
 
-func convertUrl(ctx *api.Context, chromium Api, engine gotenberg.PdfEngine, url string, options PdfOptions, mode gotenberg.SplitMode, pdfFormats gotenberg.PdfFormats, metadata map[string]any, userPassword, ownerPassword string, embedPaths []string, embedsMetadata map[string]map[string]string, facturX gotenberg.FacturX, watermark, stamp gotenberg.Stamp, rotateAngle int, rotatePages string) error {
+func convertUrl(ctx *api.Context, chromium Api, engine gotenberg.PdfEngine, url string, options PdfOptions, mode gotenberg.SplitMode, pdfFormats gotenberg.PdfFormats, metadata map[string]any, userPassword, ownerPassword string, embedPaths []string, embedsMetadata map[string]map[string]string, facturX gotenberg.FacturX, facturxXmlPath string, watermark, stamp gotenberg.Stamp, rotateAngle int, rotatePages string) error {
 	outputPath := ctx.GeneratePath(".pdf")
 	// See https://github.com/gotenberg/gotenberg/issues/1130.
 	filename := ctx.OutputFilename(outputPath)
@@ -848,6 +848,11 @@ func convertUrl(ctx *api.Context, chromium Api, engine gotenberg.PdfEngine, url
 		return err
 	}
 
+	err = pdfengines.ValidateFacturXCompat(facturX, facturxXmlPath, pdfFormats)
+	if err != nil {
+		return err
+	}
+
 	outputPaths, err := pdfengines.SplitPdfStub(ctx, engine, mode, []string{outputPath})
 	if err != nil {
 		return fmt.Errorf("split PDF: %w", err)
@@ -868,6 +873,8 @@ func convertUrl(ctx *api.Context, chromium Api, engine gotenberg.PdfEngine, url
 		return fmt.Errorf("rotate PDFs: %w", err)
 	}
 
+	pdfFormats = pdfengines.FacturXPdfFormats(ctx, engine, facturX, pdfFormats, true, nil)
+
 	convertOutputPaths, err := pdfengines.ConvertStub(ctx, engine, pdfFormats, outputPaths)
 	if err != nil {
 		return fmt.Errorf("convert PDF(s): %w", err)
@@ -890,9 +897,9 @@ func convertUrl(ctx *api.Context, chromium Api, engine gotenberg.PdfEngine, url
 		return fmt.Errorf("set embeds metadata: %w", err)
 	}
 
-	err = pdfengines.InjectFacturXXMPStub(ctx, engine, facturX, convertOutputPaths)
+	err = pdfengines.ApplyFacturXStub(ctx, engine, facturX, facturxXmlPath, convertOutputPaths)
 	if err != nil {
-		return fmt.Errorf("inject Factur-X XMP: %w", err)
+		return fmt.Errorf("apply Factur-X: %w", err)
 	}
 
 	err = pdfengines.EncryptPdfStub(ctx, engine, userPassword, ownerPassword, convertOutputPaths)

pkg/modules/exiftool/exiftool.go

@@ -528,6 +528,11 @@ func (engine *ExifTool) InjectFacturXXMP(ctx context.Context, logger *slog.Logge
 	return fmt.Errorf("inject Factur-X XMP with ExifTool: %w", gotenberg.ErrPdfEngineMethodNotSupported)
 }
 
+// ReadPdfAConformance is not available in this implementation.
+func (engine *ExifTool) ReadPdfAConformance(ctx context.Context, logger *slog.Logger, inputPath string) (string, string, error) {
+	return "", "", fmt.Errorf("read PDF/A conformance with ExifTool: %w", gotenberg.ErrPdfEngineMethodNotSupported)
+}
+
 // Interface guards.
 var (
 	_ gotenberg.Module      = (*ExifTool)(nil)

pkg/modules/libreoffice/pdfengine/pdfengine.go

@@ -140,6 +140,11 @@ func (engine *LibreOfficePdfEngine) InjectFacturXXMP(ctx context.Context, logger
 	return fmt.Errorf("inject Factur-X XMP with LibreOffice: %w", gotenberg.ErrPdfEngineMethodNotSupported)
 }
 
+// ReadPdfAConformance is not available in this implementation.
+func (engine *LibreOfficePdfEngine) ReadPdfAConformance(ctx context.Context, logger *slog.Logger, inputPath string) (string, string, error) {
+	return "", "", fmt.Errorf("read PDF/A conformance with LibreOffice: %w", gotenberg.ErrPdfEngineMethodNotSupported)
+}
+
 // Interface guards.
 var (
 	_ gotenberg.Module      = (*LibreOfficePdfEngine)(nil)

pkg/modules/libreoffice/routes.go

@@ -38,7 +38,7 @@ func convertRoute(libreOffice libreofficeapi.Uno, engine gotenberg.PdfEngine) ap
 			stampFile := pdfengines.FormDataPdfStampFile(form)
 			angle, rotatePages := pdfengines.FormDataPdfRotate(form, false)
 			embedsMetadata := pdfengines.FormDataPdfEmbedsMetadata(form)
-			facturX := pdfengines.FormDataPdfFacturX(form, false)
+			facturX, facturxXmlPath := pdfengines.FormDataPdfFacturX(form)
 
 			zeroValuedSplitMode := gotenberg.SplitMode{}
 
@@ -319,8 +319,17 @@ func convertRoute(libreOffice libreofficeapi.Uno, engine gotenberg.PdfEngine) ap
 				return err
 			}
 
+			err = pdfengines.ValidateFacturXCompat(facturX, facturxXmlPath, pdfFormats)
+			if err != nil {
+				return err
+			}
+
+			// Factur-X requires PDF/A-3; default to PDF/A-3b when no format was
+			// requested. The conversion runs as a post-processing step below.
+			pdfFormats = pdfengines.FacturXPdfFormats(ctx, engine, facturX, pdfFormats, true, nil)
+
 			hasPostProcessing := watermark.Source != "" || stamp.Source != "" || angle != 0 ||
-				len(embedPaths) > 0 || len(metadata) > 0 || flatten
+				len(embedPaths) > 0 || len(metadata) > 0 || flatten || facturX.ConformanceLevel != ""
 
 			outputPaths := make([]string, len(inputPaths))
 			for i, inputPath := range inputPaths {
@@ -504,9 +513,9 @@ func convertRoute(libreOffice libreofficeapi.Uno, engine gotenberg.PdfEngine) ap
 				return fmt.Errorf("set embeds metadata: %w", err)
 			}
 
-			err = pdfengines.InjectFacturXXMPStub(ctx, engine, facturX, outputPaths)
+			err = pdfengines.ApplyFacturXStub(ctx, engine, facturX, facturxXmlPath, outputPaths)
 			if err != nil {
-				return fmt.Errorf("inject Factur-X XMP: %w", err)
+				return fmt.Errorf("apply Factur-X: %w", err)
 			}
 
 			err = pdfengines.EncryptPdfStub(ctx, engine, userPassword, ownerPassword, outputPaths)

pkg/modules/pdfcpu/pdfcpu.go

@@ -457,6 +457,11 @@ func (engine *PdfCpu) InjectFacturXXMP(ctx context.Context, logger *slog.Logger,
 	return fmt.Errorf("inject Factur-X XMP with pdfcpu: %w", gotenberg.ErrPdfEngineMethodNotSupported)
 }
 
+// ReadPdfAConformance is not available in this implementation.
+func (engine *PdfCpu) ReadPdfAConformance(ctx context.Context, logger *slog.Logger, inputPath string) (string, string, error) {
+	return "", "", fmt.Errorf("read PDF/A conformance with pdfcpu: %w", gotenberg.ErrPdfEngineMethodNotSupported)
+}
+
 // EmbedFiles embeds files into a PDF. All files are embedded as file attachments
 // without modifying the main PDF content.
 func (engine *PdfCpu) EmbedFiles(ctx context.Context, logger *slog.Logger, filePaths []string, inputPath string) error {

pkg/modules/pdfengines/multi.go

@@ -334,6 +334,23 @@ func (multi *multiPdfEngines) InjectFacturXXMP(ctx context.Context, logger *slog
 	)
 }
 
+// ReadPdfAConformance reads the PDF/A part and conformance using the first
+// available engine that supports it.
+func (multi *multiPdfEngines) ReadPdfAConformance(ctx context.Context, logger *slog.Logger, inputPath string) (string, string, error) {
+	type pdfaConf struct {
+		part        string
+		conformance string
+	}
+	result, err := runWithFallback(ctx, "pdfengines.ReadPdfAConformance", multi.facturXEngines,
+		func(ctx context.Context, engine gotenberg.PdfEngine) (pdfaConf, error) {
+			part, conformance, err := engine.ReadPdfAConformance(ctx, logger, inputPath)
+			return pdfaConf{part: part, conformance: conformance}, err
+		},
+		func(err error) error { return fmt.Errorf("read PDF/A conformance with multi PDF engines: %w", err) },
+	)
+	return result.part, result.conformance, err
+}
+
 // Interface guards.
 var (
 	_ gotenberg.PdfEngine = (*multiPdfEngines)(nil)

pkg/modules/pdfengines/routes.go

@@ -467,12 +467,187 @@ func EmbedFilesMetadataStub(ctx *api.Context, engine gotenberg.PdfEngine, metada
 	return nil
 }
 
-// FormDataPdfFacturX extracts Factur-X parameters from form data.
-// The "facturx" field is a JSON string with the four fx properties.
-func FormDataPdfFacturX(form *api.FormData, mandatory bool) gotenberg.FacturX {
-	var facturX gotenberg.FacturX
-	form.FacturX(&facturX, mandatory)
-	return facturX
+// FormDataPdfFacturX extracts the Factur-X parameters and the invoice XML path
+// from form data. Factur-X is requested when both facturxConformanceLevel and
+// facturxXml are provided. The embedded XML always takes the canonical
+// [gotenberg.FacturXDocumentFileName] name.
+func FormDataPdfFacturX(form *api.FormData) (gotenberg.FacturX, string) {
+	var (
+		facturxXmlPath   string
+		conformanceLevel string
+		documentType     string
+		version          string
+	)
+
+	form.
+		FacturXXml(&facturxXmlPath).
+		Custom("facturxConformanceLevel", func(value string) error {
+			conformanceLevel = value
+			switch value {
+			case "",
+				gotenberg.FacturXConformanceMinimum,
+				gotenberg.FacturXConformanceBasicWL,
+				gotenberg.FacturXConformanceBasic,
+				gotenberg.FacturXConformanceEN16931,
+				gotenberg.FacturXConformanceExtended,
+				gotenberg.FacturXConformanceXRechnung:
+				return nil
+			default:
+				return fmt.Errorf("unsupported conformance level '%s'", value)
+			}
+		}).
+		Custom("facturxDocumentType", func(value string) error {
+			if value == "" {
+				documentType = gotenberg.FacturXDocumentTypeInvoice
+				return nil
+			}
+			documentType = value
+			switch value {
+			case gotenberg.FacturXDocumentTypeInvoice,
+				gotenberg.FacturXDocumentTypeOrder,
+				gotenberg.FacturXDocumentTypeOrderResponse,
+				gotenberg.FacturXDocumentTypeOrderChange:
+				return nil
+			default:
+				return fmt.Errorf("unsupported document type '%s'", value)
+			}
+		}).
+		String("facturxVersion", &version, "1.0")
+
+	return gotenberg.FacturX{
+		ConformanceLevel: conformanceLevel,
+		DocumentType:     documentType,
+		DocumentFileName: gotenberg.FacturXDocumentFileName,
+		Version:          version,
+	}, facturxXmlPath
+}
+
+// isPdfA3 reports whether the format is a PDF/A-3 variant, the only family that
+// allows the embedded files Factur-X requires.
+func isPdfA3(pdfA string) bool {
+	return pdfA == gotenberg.PdfA3a || pdfA == gotenberg.PdfA3b || pdfA == gotenberg.PdfA3u
+}
+
+// ValidateFacturXCompat enforces the Factur-X pairing and PDF/A-3 rules. It
+// returns a 400 error when the request is half-specified, or when an explicit
+// PDF/A format is not a PDF/A-3 variant.
+func ValidateFacturXCompat(facturX gotenberg.FacturX, facturxXmlPath string, pdfFormats gotenberg.PdfFormats) error {
+	if facturX.ConformanceLevel == "" && facturxXmlPath == "" {
+		return nil
+	}
+
+	if facturX.ConformanceLevel == "" {
+		return api.WrapError(
+			errors.New("facturxConformanceLevel is required when facturxXml is provided"),
+			api.NewSentinelHttpError(http.StatusBadRequest, "Invalid form data: 'facturxConformanceLevel' is required when 'facturxXml' is provided"),
+		)
+	}
+
+	if facturxXmlPath == "" {
+		return api.WrapError(
+			errors.New("facturxXml is required when facturxConformanceLevel is set"),
+			api.NewSentinelHttpError(http.StatusBadRequest, "Invalid form data: 'facturxXml' file is required when 'facturxConformanceLevel' is set"),
+		)
+	}
+
+	if pdfFormats.PdfA != "" && !isPdfA3(pdfFormats.PdfA) {
+		return api.WrapError(
+			fmt.Errorf("Factur-X requires PDF/A-3, got '%s'", pdfFormats.PdfA),
+			api.NewSentinelHttpError(http.StatusBadRequest, fmt.Sprintf("Invalid form data: Factur-X requires a PDF/A-3 variant (PDF/A-3a, PDF/A-3b, or PDF/A-3u), got '%s'", pdfFormats.PdfA)),
+		)
+	}
+
+	return nil
+}
+
+// FacturXPdfFormats returns the PDF/A formats to convert to so the output meets
+// Factur-X's PDF/A-3 requirement. It returns pdfFormats unchanged when Factur-X
+// is not requested or the caller already asked for a PDF/A-3 variant. Otherwise
+// it defaults to PDF/A-3b, except for pre-existing PDFs (sourceDoc false) that
+// already carry PDF/A-3, which are left untouched.
+func FacturXPdfFormats(ctx *api.Context, engine gotenberg.PdfEngine, facturX gotenberg.FacturX, pdfFormats gotenberg.PdfFormats, sourceDoc bool, inputPaths []string) gotenberg.PdfFormats {
+	if facturX.ConformanceLevel == "" || isPdfA3(pdfFormats.PdfA) {
+		return pdfFormats
+	}
+
+	if sourceDoc {
+		pdfFormats.PdfA = gotenberg.PdfA3b
+		return pdfFormats
+	}
+
+	// Pre-existing PDFs: keep an already-PDF/A-3 input as-is, otherwise default
+	// to PDF/A-3b.
+	for _, inputPath := range inputPaths {
+		part, _, err := engine.ReadPdfAConformance(ctx, ctx.Log(), inputPath)
+		if err != nil {
+			ctx.Log().DebugContext(ctx, fmt.Sprintf("read PDF/A conformance of '%s', assuming not PDF/A-3: %s", inputPath, err))
+			part = ""
+		}
+		if part != "3" {
+			pdfFormats.PdfA = gotenberg.PdfA3b
+			return pdfFormats
+		}
+	}
+
+	return pdfFormats
+}
+
+// ApplyFacturXStub turns each input PDF into a Factur-X document: it embeds the
+// CII invoice XML under the canonical name with AFRelationship "Alternative",
+// then injects the fx XMP metadata. The inputs must already be PDF/A-3 (see
+// [FacturXPdfFormats]). It is a no-op when Factur-X is not requested.
+func ApplyFacturXStub(ctx *api.Context, engine gotenberg.PdfEngine, facturX gotenberg.FacturX, facturxXmlPath string, inputPaths []string) error {
+	if facturX.ConformanceLevel == "" {
+		return nil
+	}
+
+	err := embedFacturXXml(ctx, engine, facturxXmlPath, inputPaths)
+	if err != nil {
+		return err
+	}
+
+	metadata := map[string]map[string]string{
+		facturX.DocumentFileName: {
+			"mimeType":     "text/xml",
+			"relationship": "Alternative",
+		},
+	}
+	err = EmbedFilesMetadataStub(ctx, engine, metadata, inputPaths)
+	if err != nil {
+		return fmt.Errorf("set Factur-X embed metadata: %w", err)
+	}
+
+	err = InjectFacturXXMPStub(ctx, engine, facturX, inputPaths)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// embedFacturXXml embeds the Factur-X invoice XML into each PDF under the
+// canonical [gotenberg.FacturXDocumentFileName] name, regardless of the
+// uploaded file name.
+func embedFacturXXml(ctx *api.Context, engine gotenberg.PdfEngine, facturxXmlPath string, inputPaths []string) error {
+	embedDir, err := ctx.CreateSubDirectory(uuid.New().String())
+	if err != nil {
+		return fmt.Errorf("create Factur-X embed subdirectory: %w", err)
+	}
+
+	canonicalPath := fmt.Sprintf("%s/%s", embedDir, gotenberg.FacturXDocumentFileName)
+	err = os.Symlink(facturxXmlPath, canonicalPath)
+	if err != nil {
+		return fmt.Errorf("symlink Factur-X invoice XML: %w", err)
+	}
+
+	for _, inputPath := range inputPaths {
+		err = engine.EmbedFiles(ctx, ctx.Log(), []string{canonicalPath}, inputPath)
+		if err != nil {
+			return fmt.Errorf("embed Factur-X invoice XML into PDF '%s': %w", inputPath, err)
+		}
+	}
+
+	return nil
 }
 
 // InjectFacturXXMPStub injects Factur-X XMP metadata into PDF files. If the
@@ -732,7 +907,7 @@ func mergeRoute(engine gotenberg.PdfEngine) api.Route {
 			stampFile := FormDataPdfStampFile(form)
 			angle, rotatePages := FormDataPdfRotate(form, false)
 			embedsMetadata := FormDataPdfEmbedsMetadata(form)
-			facturX := FormDataPdfFacturX(form, false)
+			facturX, facturxXmlPath := FormDataPdfFacturX(form)
 
 			var inputPaths []string
 			var flatten bool
@@ -760,6 +935,11 @@ func mergeRoute(engine gotenberg.PdfEngine) api.Route {
 				return err
 			}
 
+			err = ValidateFacturXCompat(facturX, facturxXmlPath, pdfFormats)
+			if err != nil {
+				return err
+			}
+
 			outputPath := ctx.GeneratePath(".pdf")
 			err = engine.Merge(ctx, ctx.Log(), inputPaths, outputPath)
 			if err != nil {
@@ -790,6 +970,8 @@ func mergeRoute(engine gotenberg.PdfEngine) api.Route {
 				}
 			}
 
+			pdfFormats = FacturXPdfFormats(ctx, engine, facturX, pdfFormats, false, outputPaths)
+
 			outputPaths, err = ConvertStub(ctx, engine, pdfFormats, outputPaths)
 			if err != nil {
 				return fmt.Errorf("convert PDF: %w", err)
@@ -856,9 +1038,9 @@ func mergeRoute(engine gotenberg.PdfEngine) api.Route {
 				return fmt.Errorf("set embeds metadata: %w", err)
 			}
 
-			err = InjectFacturXXMPStub(ctx, engine, facturX, outputPaths)
+			err = ApplyFacturXStub(ctx, engine, facturX, facturxXmlPath, outputPaths)
 			if err != nil {
-				return fmt.Errorf("inject Factur-X XMP: %w", err)
+				return fmt.Errorf("apply Factur-X: %w", err)
 			}
 
 			err = EncryptPdfStub(ctx, engine, userPassword, ownerPassword, outputPaths)
@@ -897,7 +1079,7 @@ func splitRoute(engine gotenberg.PdfEngine) api.Route {
 			stampFile := FormDataPdfStampFile(form)
 			angle, rotatePages := FormDataPdfRotate(form, false)
 			embedsMetadata := FormDataPdfEmbedsMetadata(form)
-			facturX := FormDataPdfFacturX(form, false)
+			facturX, facturxXmlPath := FormDataPdfFacturX(form)
 
 			var inputPaths []string
 			var flatten bool
@@ -923,6 +1105,11 @@ func splitRoute(engine gotenberg.PdfEngine) api.Route {
 				return err
 			}
 
+			err = ValidateFacturXCompat(facturX, facturxXmlPath, pdfFormats)
+			if err != nil {
+				return err
+			}
+
 			outputPaths, err := SplitPdfStub(ctx, engine, mode, inputPaths)
 			if err != nil {
 				return fmt.Errorf("split PDFs: %w", err)
@@ -950,6 +1137,8 @@ func splitRoute(engine gotenberg.PdfEngine) api.Route {
 				}
 			}
 
+			pdfFormats = FacturXPdfFormats(ctx, engine, facturX, pdfFormats, false, outputPaths)
+
 			convertOutputPaths, err := ConvertStub(ctx, engine, pdfFormats, outputPaths)
 			if err != nil {
 				return fmt.Errorf("convert PDFs: %w", err)
@@ -972,9 +1161,9 @@ func splitRoute(engine gotenberg.PdfEngine) api.Route {
 				return fmt.Errorf("set embeds metadata: %w", err)
 			}
 
-			err = InjectFacturXXMPStub(ctx, engine, facturX, convertOutputPaths)
+			err = ApplyFacturXStub(ctx, engine, facturX, facturxXmlPath, convertOutputPaths)
 			if err != nil {
-				return fmt.Errorf("inject Factur-X XMP: %w", err)
+				return fmt.Errorf("apply Factur-X: %w", err)
 			}
 
 			err = EncryptPdfStub(ctx, engine, userPassword, ownerPassword, convertOutputPaths)
@@ -1302,7 +1491,7 @@ func embedRoute(engine gotenberg.PdfEngine) api.Route {
 			form := ctx.FormData()
 			embedPaths := FormDataPdfEmbeds(form)
 			embedsMetadata := FormDataPdfEmbedsMetadata(form)
-			facturX := FormDataPdfFacturX(form, false)
+			facturX, facturxXmlPath := FormDataPdfFacturX(form)
 
 			var inputPaths []string
 			err := form.
@@ -1311,22 +1500,36 @@ func embedRoute(engine gotenberg.PdfEngine) api.Route {
 			if err != nil {
 				return fmt.Errorf("validate form data: %w", err)
 			}
-			err = EmbedFilesStub(ctx, engine, embedPaths, inputPaths)
+
+			err = ValidateFacturXCompat(facturX, facturxXmlPath, gotenberg.PdfFormats{})
+			if err != nil {
+				return err
+			}
+
+			// Factur-X requires PDF/A-3. Convert when needed; a no-op otherwise,
+			// so a plain embed request keeps its inputs untouched.
+			pdfFormats := FacturXPdfFormats(ctx, engine, facturX, gotenberg.PdfFormats{}, false, inputPaths)
+			outputPaths, err := ConvertStub(ctx, engine, pdfFormats, inputPaths)
+			if err != nil {
+				return fmt.Errorf("convert PDFs: %w", err)
+			}
+
+			err = EmbedFilesStub(ctx, engine, embedPaths, outputPaths)
 			if err != nil {
 				return fmt.Errorf("embed files into PDFs: %w", err)
 			}
 
-			err = EmbedFilesMetadataStub(ctx, engine, embedsMetadata, inputPaths)
+			err = EmbedFilesMetadataStub(ctx, engine, embedsMetadata, outputPaths)
 			if err != nil {
 				return fmt.Errorf("set embeds metadata: %w", err)
 			}
 
-			err = InjectFacturXXMPStub(ctx, engine, facturX, inputPaths)
+			err = ApplyFacturXStub(ctx, engine, facturX, facturxXmlPath, outputPaths)
 			if err != nil {
-				return fmt.Errorf("inject Factur-X XMP: %w", err)
+				return fmt.Errorf("apply Factur-X: %w", err)
 			}
 
-			err = ctx.AddOutputPaths(inputPaths...)
+			err = ctx.AddOutputPaths(outputPaths...)
 			if err != nil {
 				return fmt.Errorf("add output paths: %w", err)
 			}
@@ -1457,8 +1660,9 @@ func rotateRoute(engine gotenberg.PdfEngine) api.Route {
 	}
 }
 
-// facturXRoute returns an [api.Route] which injects Factur-X/ZUGFeRD XMP
-// metadata into PDF/A-3 files.
+// facturXRoute returns an [api.Route] which turns existing PDFs into Factur-X
+// documents: it ensures PDF/A-3, embeds the CII invoice XML, and injects the fx
+// XMP metadata.
 func facturXRoute(engine gotenberg.PdfEngine) api.Route {
 	return api.Route{
 		Method:      http.MethodPost,
@@ -1468,7 +1672,8 @@ func facturXRoute(engine gotenberg.PdfEngine) api.Route {
 			ctx := c.Get("context").(*api.Context)
 
 			form := ctx.FormData()
-			facturX := FormDataPdfFacturX(form, true)
+			pdfFormats := FormDataPdfFormats(form)
+			facturX, facturxXmlPath := FormDataPdfFacturX(form)
 
 			var inputPaths []string
 			err := form.
@@ -1478,12 +1683,32 @@ func facturXRoute(engine gotenberg.PdfEngine) api.Route {
 				return fmt.Errorf("validate form data: %w", err)
 			}
 
-			err = InjectFacturXXMPStub(ctx, engine, facturX, inputPaths)
-			if err != nil {
-				return fmt.Errorf("inject Factur-X XMP into PDFs: %w", err)
+			// Factur-X is the whole point of this route, so both fields are
+			// mandatory here.
+			if facturX.ConformanceLevel == "" || facturxXmlPath == "" {
+				return api.WrapError(
+					errors.New("facturxConformanceLevel and facturxXml are required"),
+					api.NewSentinelHttpError(http.StatusBadRequest, "Invalid form data: 'facturxConformanceLevel' and 'facturxXml' are both required"),
+				)
 			}
 
-			err = ctx.AddOutputPaths(inputPaths...)
+			err = ValidateFacturXCompat(facturX, facturxXmlPath, pdfFormats)
+			if err != nil {
+				return err
+			}
+
+			pdfFormats = FacturXPdfFormats(ctx, engine, facturX, pdfFormats, false, inputPaths)
+			outputPaths, err := ConvertStub(ctx, engine, pdfFormats, inputPaths)
+			if err != nil {
+				return fmt.Errorf("convert PDFs: %w", err)
+			}
+
+			err = ApplyFacturXStub(ctx, engine, facturX, facturxXmlPath, outputPaths)
+			if err != nil {
+				return fmt.Errorf("apply Factur-X: %w", err)
+			}
+
+			err = ctx.AddOutputPaths(outputPaths...)
 			if err != nil {
 				return fmt.Errorf("add output paths: %w", err)
 			}

pkg/modules/pdftk/pdftk.go

@@ -505,6 +505,11 @@ func (engine *PdfTk) InjectFacturXXMP(ctx context.Context, logger *slog.Logger,
 	return fmt.Errorf("inject Factur-X XMP with PDFtk: %w", gotenberg.ErrPdfEngineMethodNotSupported)
 }
 
+// ReadPdfAConformance is not available in this implementation.
+func (engine *PdfTk) ReadPdfAConformance(ctx context.Context, logger *slog.Logger, inputPath string) (string, string, error) {
+	return "", "", fmt.Errorf("read PDF/A conformance with PDFtk: %w", gotenberg.ErrPdfEngineMethodNotSupported)
+}
+
 // Interface guards.
 var (
 	_ gotenberg.Module      = (*PdfTk)(nil)

pkg/modules/qpdf/facturx_test.go

@@ -247,3 +247,53 @@ func assertContains(t *testing.T, haystack, needle string) {
 		t.Errorf("expected output to contain %q", needle)
 	}
 }
+
+func TestParsePdfAId(t *testing.T) {
+	for _, tc := range []struct {
+		scenario      string
+		xmp           string
+		expectPart    string
+		expectConform string
+	}{
+		{
+			scenario:      "element form",
+			xmp:           `<rdf:Description><pdfaid:part>3</pdfaid:part><pdfaid:conformance>B</pdfaid:conformance></rdf:Description>`,
+			expectPart:    "3",
+			expectConform: "B",
+		},
+		{
+			scenario:      "attribute form",
+			xmp:           `<rdf:Description pdfaid:part="3" pdfaid:conformance="U"></rdf:Description>`,
+			expectPart:    "3",
+			expectConform: "U",
+		},
+		{
+			scenario:      "part 2",
+			xmp:           `<pdfaid:part>2</pdfaid:part><pdfaid:conformance>B</pdfaid:conformance>`,
+			expectPart:    "2",
+			expectConform: "B",
+		},
+		{
+			scenario:      "no pdfa identification",
+			xmp:           `<rdf:Description><dc:title>foo</dc:title></rdf:Description>`,
+			expectPart:    "",
+			expectConform: "",
+		},
+		{
+			scenario:      "empty packet",
+			xmp:           "",
+			expectPart:    "",
+			expectConform: "",
+		},
+	} {
+		t.Run(tc.scenario, func(t *testing.T) {
+			part, conformance := parsePdfAId(tc.xmp)
+			if part != tc.expectPart {
+				t.Errorf("expected part %q but got %q", tc.expectPart, part)
+			}
+			if conformance != tc.expectConform {
+				t.Errorf("expected conformance %q but got %q", tc.expectConform, conformance)
+			}
+		})
+	}
+}

pkg/modules/qpdf/qpdf.go

@@ -12,6 +12,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"regexp"
 	"strings"
 	"syscall"
 
@@ -729,6 +730,68 @@ func (engine *QPdf) InjectFacturXXMP(ctx context.Context, logger *slog.Logger, f
 	return nil
 }
 
+// ReadPdfAConformance reads the PDF/A part and conformance from the
+// document-level XMP packet (pdfaid:part and pdfaid:conformance) using QPDF's
+// JSON output. It returns empty strings when the document carries no XMP
+// metadata stream or no PDF/A identification.
+func (engine *QPdf) ReadPdfAConformance(ctx context.Context, logger *slog.Logger, inputPath string) (string, string, error) {
+	ctx, span := gotenberg.Tracer().Start(ctx, "qpdf.ReadPdfAConformance",
+		trace.WithSpanKind(trace.SpanKindClient),
+		trace.WithAttributes(semconv.ServerAddress(engine.binPath)),
+	)
+	defer span.End()
+
+	logger.DebugContext(ctx, fmt.Sprintf("reading PDF/A conformance from %s with QPDF", inputPath))
+
+	args := append([]string{inputPath}, engine.globalArgs...)
+	args = append(args, "--json-output", "--json-stream-data=inline")
+
+	output, err := engine.execCaptureOutput(ctx, args...)
+	if err != nil {
+		err = fmt.Errorf("get PDF JSON with QPDF: %w", err)
+		span.RecordError(err)
+		span.SetStatus(codes.Error, err.Error())
+		return "", "", err
+	}
+
+	objects, err := parsePdfObjects(output)
+	if err != nil {
+		span.RecordError(err)
+		span.SetStatus(codes.Error, err.Error())
+		return "", "", err
+	}
+
+	_, _, xmp, err := findMetadataStream(objects)
+	if err != nil {
+		// No XMP metadata stream means no PDF/A identification.
+		logger.DebugContext(ctx, fmt.Sprintf("no XMP metadata stream in %s: %s", inputPath, err))
+		span.SetStatus(codes.Ok, "")
+		return "", "", nil
+	}
+
+	part, conformance := parsePdfAId(xmp)
+	span.SetStatus(codes.Ok, "")
+	return part, conformance, nil
+}
+
+var (
+	pdfaIdPartRe        = regexp.MustCompile(`pdfaid:part[\s>="']*([0-9]+)`)
+	pdfaIdConformanceRe = regexp.MustCompile(`pdfaid:conformance[\s>="']*([A-Za-z]+)`)
+)
+
+// parsePdfAId extracts the PDF/A part and conformance from an XMP packet. It
+// handles both the element (<pdfaid:part>3</pdfaid:part>) and attribute
+// (pdfaid:part="3") serializations.
+func parsePdfAId(xmp string) (part string, conformance string) {
+	if m := pdfaIdPartRe.FindStringSubmatch(xmp); m != nil {
+		part = m[1]
+	}
+	if m := pdfaIdConformanceRe.FindStringSubmatch(xmp); m != nil {
+		conformance = m[1]
+	}
+	return part, conformance
+}
+
 // validateFacturX checks the Factur-X fields against the supported values.
 func validateFacturX(facturX gotenberg.FacturX) error {
 	switch facturX.ConformanceLevel {
@@ -930,7 +993,7 @@ func facturXSchemaLi() string {
          <pdfaProperty:name>DocumentType</pdfaProperty:name>
          <pdfaProperty:valueType>Text</pdfaProperty:valueType>
          <pdfaProperty:category>external</pdfaProperty:category>
-         <pdfaProperty:description>INVOICE</pdfaProperty:description>
+         <pdfaProperty:description>The type of the embedded Factur-X document</pdfaProperty:description>
         </rdf:li>
         <rdf:li rdf:parseType="Resource">
          <pdfaProperty:name>Version</pdfaProperty:name>

test/integration/features/libreoffice_convert.feature

@@ -714,27 +714,29 @@ Feature: /forms/libreoffice/convert
     Then the response PDF(s) should have the "embed_1.xml" file embedded
     Then the response PDF(s) should have the "embed_2.xml" file embedded
 
+  # A Factur-X request supplies the invoice XML via facturxXml plus the
+  # facturxConformanceLevel; Gotenberg owns the PDF/A-3, the Alternative
+  # relationship, and the canonical factur-x.xml name. No explicit pdfa here
+  # exercises the automatic PDF/A-3b default for a source document.
   @convert
-  @embed
   @factur-x
   Scenario: POST /forms/libreoffice/convert (Factur-X / ZUGFeRD)
     Given I have a default Gotenberg container
     When I make a "POST" request to Gotenberg at the "/forms/libreoffice/convert" endpoint with the following form data and header(s):
-      | files                     | testdata/page_1.docx                                                 | file   |
-      | pdfa                      | PDF/A-3b                                                             | field  |
-      | embeds                    | testdata/embed_1.xml                                                 | file   |
-      | embedsMetadata            | {"embed_1.xml":{"mimeType":"text/xml","relationship":"Alternative"}} | field  |
-      | facturx                   | {"conformanceLevel":"EN 16931"}                                      | field  |
-      | Gotenberg-Output-Filename | foo                                                                  | header |
+      | files                     | testdata/page_1.docx | file   |
+      | facturxXml                | testdata/embed_1.xml | file   |
+      | facturxConformanceLevel   | EN 16931             | field  |
+      | Gotenberg-Output-Filename | foo                  | header |
     Then the response status code should be 200
     Then the response header "Content-Type" should be "application/pdf"
     Then there should be 1 PDF(s) in the response
     Then the response PDF(s) should be valid "PDF/A-3b" with a tolerance of 0 failed rule(s)
-    Then the response PDF(s) should have the "embed_1.xml" file embedded with relationship "Alternative"
+    Then the response PDF(s) should have the "factur-x.xml" file embedded with relationship "Alternative"
     Then the response PDF(s) should declare Factur-X XMP with conformance level "EN 16931"
 
+  # The base PDF is already PDF/A-3b: detection keeps it as-is, no reconversion.
   @factur-x
-  Scenario: POST /forms/pdfengines/factur-x (Standalone)
+  Scenario: POST /forms/pdfengines/factur-x (Standalone, already PDF/A-3)
     Given I have a default Gotenberg container
     When I make a "POST" request to Gotenberg at the "/forms/libreoffice/convert" endpoint with the following form data and header(s):
       | files                     | testdata/page_1.docx | file   |
@@ -742,15 +744,45 @@ Feature: /forms/libreoffice/convert
       | Gotenberg-Output-Filename | base                 | header |
     Then the response status code should be 200
     When I make a "POST" request to Gotenberg at the "/forms/pdfengines/factur-x" endpoint with the following form data and header(s):
-      | files                     | teststore/base.pdf                                  | file   |
-      | facturx                   | {"conformanceLevel":"BASIC","documentType":"ORDER"} | field  |
-      | Gotenberg-Output-Filename | foo                                                 | header |
+      | files                     | teststore/base.pdf   | file   |
+      | facturxXml                | testdata/embed_1.xml | file   |
+      | facturxConformanceLevel   | BASIC                | field  |
+      | facturxDocumentType       | ORDER                | field  |
+      | Gotenberg-Output-Filename | foo                  | header |
     Then the response status code should be 200
     Then the response header "Content-Type" should be "application/pdf"
     Then there should be 1 PDF(s) in the response
     Then the response PDF(s) should be valid "PDF/A-3b" with a tolerance of 0 failed rule(s)
+    Then the response PDF(s) should have the "factur-x.xml" file embedded with relationship "Alternative"
     Then the response PDF(s) should declare Factur-X XMP with conformance level "BASIC"
 
+  # The base PDF is not PDF/A: detection converts it to PDF/A-3b automatically.
+  @factur-x
+  Scenario: POST /forms/pdfengines/factur-x (Standalone, converts non-PDF/A input)
+    Given I have a default Gotenberg container
+    When I make a "POST" request to Gotenberg at the "/forms/libreoffice/convert" endpoint with the following form data and header(s):
+      | files                     | testdata/page_1.docx | file   |
+      | Gotenberg-Output-Filename | plain                | header |
+    Then the response status code should be 200
+    When I make a "POST" request to Gotenberg at the "/forms/pdfengines/factur-x" endpoint with the following form data and header(s):
+      | files                     | teststore/plain.pdf  | file   |
+      | facturxXml                | testdata/embed_1.xml | file   |
+      | facturxConformanceLevel   | EN 16931             | field  |
+      | Gotenberg-Output-Filename | foo                  | header |
+    Then the response status code should be 200
+    Then the response PDF(s) should be valid "PDF/A-3b" with a tolerance of 0 failed rule(s)
+    Then the response PDF(s) should have the "factur-x.xml" file embedded with relationship "Alternative"
+    Then the response PDF(s) should declare Factur-X XMP with conformance level "EN 16931"
+
+  # facturxConformanceLevel without facturxXml is a half-specified request.
+  @factur-x
+  Scenario: POST /forms/pdfengines/factur-x (Bad Request)
+    Given I have a default Gotenberg container
+    When I make a "POST" request to Gotenberg at the "/forms/pdfengines/factur-x" endpoint with the following form data and header(s):
+      | files                   | testdata/page_1.pdf | file  |
+      | facturxConformanceLevel | EN 16931            | field |
+    Then the response status code should be 400
+
   # FIXME: once decrypt is done, add encrypt and check after the content of the PDF.
   @convert
   @metadata