I found this information on the Tor website:
You should be very careful when downloading documents via Tor
(especially DOC and PDF files) as these documents can contain Internet
resources that will be downloaded outside of Tor by the application
that opens them. This will reveal your non-Tor IP address. If you must
work with DOC and/or PDF files, we strongly recommend either using a
disconnected computer, downloading the free VirtualBox and using it
with a virtual machine image with networking disabled, or using Tails.
Under no circumstances is it safe to use BitTorrent and Tor together,
Images can not be embedded from an external source as far as I know. So which resources are meant?