I'm currently trying to organize my files and one thing that would be useful is adding metadata to all my pdfs (to other document types would be useful too) so I can search through them easily. But the title and author tags aren't quite enough. Is there any way to add custom tags like subtitle, edition, volume, original publication date, etc to pdf files? Bonus points if it also works on djvu files.
Forgot to mention: I'm running Linux Mint and so can't run Adobe Reader/ Acrobat (... well I suppose I could with Wine but I'd prefer a native solution).