[jcrawfordx]

@Kovid- This worked great! (I have decided to call this nulll format as "@PAPER" instead of "paperbook" as originally cited.)

Here's what I did: I selected the target book listings, then "Add Books" --> "Add files to selected records", navigated to my test.@PAPER file, pulled down the file type dropdown, selected "all files" and then selected my test.@PAPER file. BINGO! It added "@PAPER" for the format columns for my selected books. Very nice! :-)
Also noticed that Shift+A from main Calibre screen is a shortcut for this. MARVELOUS!

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@Better Red - Installing the icon did not work. I did as you said, but in the Edit Metadata screen in the Formats box (upper right corner) my "@PAPER" format showed up as text (as 0.00 MB size), but the icon to the left of it just has a question mark in it. It's not my @PAPER icon.

I had placed a 128x128 version of "@PAPER.png" in C:\Program Files\Calibre2\app\resources\images\mimetypes.

Do I need to "install" it in some config or something?

Thanks to both of you for your help with this!