Mac OS Books Categories from PDFs

I happen to store a large amount of PDFs in my Books library - which is generally great for references/papers, tech manuals, etc., and although I know we cannot readily create nor alter those category titles... They are somehow being generated from embedded data of the documents. A few of my downloaded and "print-to PDFs" are generating odd category names. So, I was wondering if there might be any way to possibly re-categorize them – generally guessing: No... Or perhaps edit that data within the PDF, directly? Odd one, I know... but appreciated. Much Thanks!