[KevinH]

An eReader *.pdb book is encoded by the last 8 digits of the credit card number and the the name on the credit card. That is what eReader / Barnes & Noble" calls "social drm". If you bought the book yourself, you should have that information.

The idea is that people would be unwilling to give away the credit card number and the name on the credit card, to others so that the book (while in its DRM form) is safe from theft.

In contrast, Mobipocket/Kindle uses a PID and you could in fact give the PID to others along with the DRM'd book if you wanted someone else to read it.

Your own eReader program should ask you for that same information (actually they want the entire cc number!) and the name on the credit card when you try to open that book for the first time (or already has and has kept it stored someplace).