I'd love to see this implemented in the Roll20 app.
It's very useful to show PDF files to your players in midst of a game --references to rules, story background sections in manuals, character sheets . . . I think that be able to handle virtual books inside a virtual tabletop is essential because, after all, books are so essential to face to face role playing as to be able to behold the faces of your friends --which is currently supported via webcam.
If there are concerns about they downloading or copyring copyrighted PDF books, it would be possible only to dynamically share the PDF, emulating the way you show a real, physical book to your players around a table during a game session: when you go home again, you carry your book with you, without making copies nor indulging into piracy.
This is doable by means of a "Screen sharing", making you to select your PDF app (FoxitReader, Acrobat Reader, whatever) and streaming it to the players in real time. Currently Google+ Hangout allows this, but I find a number of drawbacks in them so I'd love to see this feature implemented inside Roll20.
For what is worth, the last update of the Join.Me app (<a href="https://join.me/" rel="nofollow">https://join.me/</a>) also allows "Screen sharing" not of the entire desktop, but of a selected window or app running in your system. The drawback is that this feature is only available in the Pro version, which isn't free nor cheap --on the other hand, it works much better than the "Screen sharing" feature available for Google+ Hangouts.
