Sync coordinated in app, eg, pdf annotation instantly shared with group

I’m using Juris-M (Zotero fork) for managing legal citations and research notes. When the zotfile extension is also loaded, it can put pdf onto my tablet for reading and annotation. It would be cool if when working in a group, each person’s annotations are instantly synced to each others, and with syncthing so no server is required. I wish somebody with time and knowledge would make a pdf annotate program do that.

Maybe by just saving the file after making a note in it would suffice… as long as the reader program can refresh and not lose local annotations when both updates are near each other temporally or in the same part of the document.