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ddjohn - you probably don't need a plugin.
You you can add any file type to calibre, but for non ebook file types -- i.e.
not in
Preferences->Behaviour->Use internal view for -- there is limited functionality - no conversion, no editor, no metadata download etc.
You can only have one file of any type in a 'book' - so only one .VP3, only one .PES, etc.
If the file type has an OS file association, then calibre will use it as a 'viewer'. Within calibre you can associate other programs with a file type, in this recent post
284, you can see I have added Balabolka, Sigil and WinRAR to EPUBS via calibre's Open With option, and in that example you can see I have a .ONE file (from MS OneNote) for the book.
You may have to add the cover images manually, which is easy enough, just drop an image file into the Book Details sidebar on the right (bottom if configured thus)
If all the files for a given pattern are in separate folders you can use one of the
Add Books from directories options.
I have calibre.exe in my Windows Send To folder, to add a book(s) I select the file (e.g. an FLV) in File Manager, navigate to Send To->calibre in Windows context menu and hit enter -- I always edit the file name to be 'Author - Title' to match my Add Books template.
If you're mouse centric you can drag and drop the file(s) into the book list. To add a file to an existing book I drag and drop the file into the Book Details sidebar - file names are irrelevant in this instance.
BR