I'm trying to organize a collection of maybe 500 or so journal articles, stored in a combination of .pdf and .djvu formats. I'd like to be able to sort the collection by author(s), title, journal name, year, and subject keywords. Is there a way to create metadata fields for this information in the Windows file system (similar to how .mp3 files come with tags for album, title, track length, etc)? Or, if not, is there some software (preferably free) that can do something similar?