Some are 'just pictures.'
I get fax documents via e-mail all the time, and they come as a series of pages scanned as graphic files and stored in a pdf file.
On the other hand, optical character recognition software can scan a page, convert it to text and store it in an editable form as a series of characters, again, in a pdf file.
It can be done either way.
The SeeBS documents are images stored in a pdf, not characters.
Is there something about these files that tells you this? I get pdf files all the time with graphics and such - the graphics don't change, but I can edit the text. When the scanned doc is in some typeface that I don't have in Adobe, it swaps to my defaults.