LibreOffice: tagged PDF without declaring PDF/UA conformance #1676

Hi @gulien, thanks for Gotenberg! We run both the Chromium and the LibreOffice routes for regulated documentation, and it's been a great fit.

This is a follow-up to #1481. The answer there was that tagging is available through pdfua, and it is. But pdfua=true also declares PDF/UA-1 conformance in the XMP metadata (pdfuaid:part=1). We convert arbitrary user documents (images without alt text, no real heading structure, and so on), so we can't guarantee that conformance. We'd rather ship a tagged PDF that makes no claim than a claim that may be false.

Reproduction on gotenberg/gotenberg:8.37.0-libreoffice with a plain .docx:

LibreOffice exposes the two settings separately (UseTaggedPDF and PDFUACompliance). Gotenberg already makes the same distinction on the Chromium routes: generateTaggedPdf (added after #1210) next to pdfua.

Proposal: a generateTaggedPdf form field on /forms/libreoffice/convert, false by default, so nothing changes for existing requests. When it's true and pdfua is not set, Gotenberg passes UseTaggedPDF=true and keeps PDFUACompliance=false. pdfua=true keeps implying tagging, as it does today.

I have a small PR ready and will link it here. Happy to change the name or the approach, or to close it if you'd rather not add another field.