I tried removing the protection using off the shelf products. they remove the protection, but also remove the entire contents of the doc
Injecting the user info could be done at download time. I have made quite a few web sites that do this and have the PDF creation components on my server, however I have notlooked into copy protection usung this system as it never has been a requirement. For more info on the component I am using look at
http://www.asppdf.com/