Description of Changes

TLDR

• Updated PdfToPdfARequest to include PDF/X in supported output formats
• Expanded input handling and model validation for PDF/A and PDF/X
• Added Ghostscript as a preferred backend for PDF/A and PDF/X conversions
• Implemented PDF/X-specific conversion logic with detailed validation
• Updated UI templates to separate PDF/A and PDF/X format options
• Updated error handling and warnings during conversion processes

This PR replaces the PDF/A conversion system with Ghostscript as the primary method, which less warning prone output compared to the previous LibreOffice approach. It also adds PDF/X format support for print production workflows.

Better PDF/A Compliance

• Ghostscript produces standards-compliant PDF/A with fewer validation errors
• Previous LibreOffice method generates files with structural errors and validation warnings
• Automatic fallback to PDFBox/LibreOffice if Ghostscript unavailable
• Built-in validation using PDFBox Preflight catches issues early

New PDF/X Support

Print production workflows now supported with PDF/X-1, PDF/X-3, and PDF/X-4 formats for professional printing requirements.

More Reliable Output

• Deterministic conversion results
• Better font embedding and subsetting
• Proper ICC profile and color space handling
• Improved resource cleanup prevents memory leaks

Ghostscript Integration

• buildGhostscriptCommand() / buildGhostscriptCommandX() - Constructs CLI arguments
• convertWithGhostscript() / convertWithGhostscriptX() - Executes conversion
• isGhostscriptAvailable() - Checks installation
• prepareColorProfiles() - Sets up ICC profiles
• createPdfaDefFile() - Generates PostScript definitions

Conversion Flow

• handlePdfAConversion() - Routes PDF/A with Ghostscript primary, PDFBox fallback
• handlePdfXConversion() - Routes PDF/X using Ghostscript
• convertWithPdfBoxMethod() - Refactored fallback method

Validation

• validatePdfaOutput() - Validates using PDFBox Preflight
• validateAndWarnPdfA() - Logs warnings instead of failing
• buildPreflightErrorMessage() - Formats detailed errors

Font Handling

Updated embedMissingFonts() prevents stream exhaustion by loading font bytes once and creating fresh InputStreams for multiple load attempts.

Utilities

• findUnembeddedFontNames() - Identifies unembedded fonts
• deleteQuietly() - Recursively deletes temp directories
• sanitizePdfA() - Removes incompatible elements
• removeElementsForPdfA() - Removes Optional Content and transparency
• mergeAndAddXmpMetadata() - Handles XMP metadata
• preProcessHighlights() - Pre-processes annotations
• Transparency detection: isTransparencyGroup(), hasTransparentImages(), detectTransparentXObjects()

PDF/A

• PDF/A-1b: Strict compliance
• PDF/A-2b: Extended features (default)
• PDF/A-3b: Embedded files support

PDF/X

• PDF/X-1: Standard print exchange
• PDF/X-3: Color-managed with ICC profiles
• PDF/X-4: Transparency support

As mentioned greatest benefit is the new Ghostscript conversion is able to deliver fewer warning/zero error PDF/A files compared to the LibreOffice. Sometimes however, both succeed without warnings. Here are some samples:

There is also some size difference, (not sure why) but generally that also favors Ghostscript:

Front-end

Checklist

General

• I have read the Contribution Guidelines
• I have read the Stirling-PDF Developer Guide (if applicable)
• I have read the How to add new languages to Stirling-PDF (if applicable)
• I have performed a self-review of my own code
• My changes generate no new warnings

Documentation

• I have updated relevant docs on Stirling-PDF's doc repo (if functionality has heavily changed)
• I have read the section Add New Translation Tags (for new translation tags only)

Translations (if applicable)

• I ran scripts/counter_translation.py

UI Changes (if applicable)

• Screenshots or videos demonstrating the UI changes are attached (e.g., as comments or direct attachments in the PR)

Testing (if applicable)

• I have tested my changes locally. Refer to the Testing Guide for more details.