[tor-relays] About TBB downloadings

[Lluís]

In the web page here:

https://www.torproject.org/download/download.html.en#warning

advises us not to
"... open documents downloaded through Tor while online"

Many technical manuals and scientific papers are written in
pdf format, and I usually read them.

So my question is:

Is it safe to download them with TBB first and then
open them with, say, "Document Viewer" ?

Where can I find more information about it ?

Lluís,
Spain