You should check out hyperpaper, and maybe let's build an obsidian plugin with similar functionality. The problem right now with obsidian is pen input lag atleast on my Onyx device.
The idea I want to eventually pursue is set up a service where you could sync your pdf (or send specific pages via email), have them OCRed (including dates and titles specifically since they already live in well-defined parts of the pages), and then ingest them into your PKM for long-term storage and recall
Unfortunately Obsidian Cloud doesn't seem to have an API to support this at present, but I think it's theoretically feasible with Notion at least. Let me know if you build something like this :)