PDF/Document annotation support

I think it’d be great if RemNote supported the ability to import document annotations (e.g. from PDFs, Word documents, etc.), in the same way that LiquidText, MarginNote or Polar Bookshelf do, and then using the annotation content to generate flashcards from Rems in a similar way to how it currently makes Rems out of Anki cards.

Aligns closely with the idea of explicitly implementing incremental reading, and this previous feature request for having PDF support.