feat: add PDF encryption feature (#1217)

* Adding PDF encryption option

* LibreOffice
* QPDF
* PDFtk
* pdfcpu

* Update pkg/modules/pdfengines/pdfengines.go

Co-authored-by: Julien Neuhart <neuhart.julien@gmail.com>

* npx prettier

* go fmt

* PR comments

* Update test/integration/scenario/scenario.go

Co-authored-by: Julien Neuhart <neuhart.julien@gmail.com>

* renamed ProtectWithPassword to encrypt

* more clean up

* Use the same input path as requested

* This commit completes the encryption implementation

* Clean up. Added webhook, disable route and download from tests

---------

Co-authored-by: Julien Neuhart <neuhart.julien@gmail.com>

pkg/modules/pdftk/pdftk.go

@@ -145,6 +145,43 @@ func (engine *PdfTk) WriteMetadata(ctx context.Context, logger *zap.Logger, meta
 	return fmt.Errorf("write PDF metadata with PDFtk: %w", gotenberg.ErrPdfEngineMethodNotSupported)
 }
 
+// Encrypt adds password protection to a PDF file using PDFtk.
+func (engine *PdfTk) Encrypt(ctx context.Context, logger *zap.Logger, inputPath, userPassword, ownerPassword string) error {
+	if userPassword == "" {
+		return errors.New("user password cannot be empty")
+	}
+
+	// If owner password is not provided, use the user password as owner password
+	if ownerPassword == "" {
+		ownerPassword = userPassword
+	}
+
+	var args []string
+	args = append(args, inputPath)
+	args = append(args, "output", inputPath)
+	args = append(args, "encrypt_128bit")
+
+	if userPassword != "" {
+		args = append(args, "user_pw", userPassword)
+	}
+
+	if ownerPassword != "" {
+		args = append(args, "owner_pw", ownerPassword)
+	}
+
+	cmd, err := gotenberg.CommandContext(ctx, logger, engine.binPath, args...)
+	if err != nil {
+		return fmt.Errorf("create command: %w", err)
+	}
+
+	_, err = cmd.Exec()
+	if err != nil {
+		return fmt.Errorf("encrypt PDF with PDFtk: %w", err)
+	}
+
+	return nil
+}
+
 // Interface guards.
 var (
 	_ gotenberg.Module      = (*PdfTk)(nil)