Lluís wrote:
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.
The reason for this is that offline applications can leak information outside of Tor. If the file downloaded contained an identifier unique to your Tor connection, and an application outside of that Tor connection leaked the identifier, then it would breach anonymity.
For example, if you downloaded a HTML page as a file and an image contained a unique ID this could occur.
To answer your question (or not really):
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 ?
I'm not sure whether Evince (I'm assuming this is what you're referring to) leaks information, e.g. downloading of external resources.
By the way, Tails solves this problem by forcing all applications to go through Tor.