I hadn't ever thought about this, but now that I'm seeing your post, it would be a good idea. Will try it with my JB'd AppleTV now.
Just tried via the aTV Flash Black media player, and did not work. Tried using the aTV Flash web browser, and I could not view a .pdf file. Funny thing is, if I did a 'Quick Preview' of the .pdf in Google I could see the document, but I was not able to navigate through it, i.e. scroll up, down, left, right. I could zoom in, but could not zoom out.
So technically no, you can't at the moment, even with a jailbroken device.