We were able to open a PDF in LibreOffice and edit text and add text and images. We weren’t able to add a signature, but this would be simple enough if you already had the signature as an image ...
The base version of LibreOffice doesn’t support online document editing at all ... Documents can also be exported to PDF, Microsoft Word format, or OpenDocument format (ODF).
FOSDEM 2025 LibreOffice ... [PDF], which explains that this is achieved using CRDTs, or conflict-free replicated data types – the same tech whose use we described in the Zed programmer's editor ...