There is a lot out there... http://www.phpclasses.org/package/1370- ... mages.html
but a thumb of pdf, or doc maybe harder...
I like the way this system shares files, folders, notes, etc. (right click, share). They have a few features that would be good in pb, like email, calendar, notes, tasks, announcements, and a fairly good file system for documents. - http://www.group-office.com/
This system (cmsms) has a good and simple file manager - http://www.cmsmadesimple.org/