I am becoming more and more interested in making Personal Books for Logos. With my 9 grandchildren and other family issues, I just don't have as much money to spend for my Logos library as I have in the past, and I really love some of the unique and older material available.
Many public domain works in PDF format that would be great Personal Books for Logos are actually scanned images of the pages, not text based. Thus, they are not searchable in Logos.
I have used and recommended the Adobe online subscription service to convert PDF files to Docx format for personal books. It is cheap and very good, and who knows more about PDF than Adobe?
But it's not very good for those scanned PDF files that are images of the page and not text based. They have to be converted into text first, and Calibre does not do that either.
The very best solution I have found for that is Omnipage 18 OCR. It does a nice job. Still requires some editing, but is quite good. If you search hard on the internet you can get Omnipage 18 (as a download) pretty cheap - like less than half price.