Move the documents that are papers to /usr/share/doc/papers.
Give them suitable names (including the author and year).
The key property of papers that distinguishes them from documentation
is that they're historical: they're published at a particular time and
aren't updated or maintained. (Except cosmetically.)
We should only ship papers that are of interest to users, either for
historical perspective or because they're the original research
writeup of stuff that went into the system and is still pertinent.
The ffs papers clearly meet this standard; the other one here (about
passwords, in 1978) is probably past its sell-by date.