Enter my PDFs and other ebooks (Amazon, etc.) into this program. At least, PDFs --- this is a must for me.

Only entering "paper" books is fine if we we back in the 70s or 80s. But that was a long time ago. To be relevant, this program must --- at the very least --- be able to read a PDF. If that is too difficult to start with, then let it at least put in the file name of the PDF and look that up.