I have found that .PDF documents are usually downloadable from the company or persons that created it off their own website. You should check the host and if you can (if bearshare allows you to chat with host) ask them where they got it from. Be careful though because some people beleive that it is legal to download files from places like Bearshare and Limewire because they are sharing files, but it isnt as the files will still be copywritten!
sam