If there are not relevant discussions at:

http://absolutewrite.com/forums/index.php

I suspect you could start one.

These people are in the space:

http://www.pdf-publishing.com/

I used their Drumlin to DRM some study guides I wrote few years ago. The Drumlin product is here:

http://www.drumlinsecurity.com/index.html

I will say that they appear to have their roots in publishing and are using technology to further their domain expertise rather than trying to work the problem the other way. A lack of publishing domain expertise is, in my opinion, likely to be a major hurdle for certain types of work. For something like Scribd, not so much.