Bro! I just came on this subreddit right now, to ask about the very same situation! In my case, I have well over 900 PDF documents, which a lot of them i transfered from my phone to computer. Then a good majority of them are full books, which I’ved OCR-processed and then turned into ebook format for Calibre web-server.

But the others are legal documents, tax documents, instruction manuals, research papers, etc.