Tried really hard to figure out for myself, and search for answers, but am failing badly. In organizing my library (the vast majority epubs), I've got several PDFs that I've (understanding the extreme difficulty of even converting PDF to PDF) used Adobe Pro (File/Properties) to put in my title, author in preferred format ("Last, First") and used the Subject field for my preferred Tag (which is how I organize: WorldLit, Bios, Etc). This has worked well, so that the PDF can be dragged into a new Calibre library and the tag and author name/order is how I want it.

Anyway, I want to change some of the Tags to match some changes I made to the Epubs. For instance, changing "NonFiction.Bios" to "Biographies & Memoirs". Here's where I'm going nuts. While I've changed the Subject field to the new Tag in Adobe, when I drag the updated PDF into a new Library, both the new AND the old tags appear. So, I've also opened the PDF in Notepad+, and found the old tag in there (as a keyword, in the description section near bottom) and deleted. Still the same result, EVEN after uninstalling Calibre and deleting any remnants of it that I could find>> my thinking here is that if the words "NonFiction.Bios" aren't anywhere in the PDFs properties or the file itself, Calibre must be "remembering" something about the PDF, but I can't figure out where.

The bottom line is that I want to have the PDFs in my library be standalone with my title, author and tags, so that the single file can be put in anyone's Calibre library and the Tag will be as I left it (and not need adjusted again in the library).

Hope this makes sense, and imagine I'm just doing something dumb, so quite humbly grateful for anyone's help here! Thank you.