There's Fermat's Library [1] which allows for collaborative annotation on pdfs. The only issue I have with them is that they lack highlighting and aren't open s

There's Fermat's Library [1] which allows for collaborative annotation on pdfs. The only issue I have with them is that they lack highlighting and aren't open source. With PDF annotation, why not separate the content from the content representation? Have an editor for the original content, and export to pdf. If people want to annotate, give the original content or a copy. Easier to version control this way as well. [1] https://fermatslibrary.com/ https://fermatslibrary.com/