I have the same problem. I don't know about the others, but Beamreader did not solve it for me.
I placed the certificate file (.pfx) and the pdf in the same folder in my Motorola Xoom, then installed Beamreader and tried to open the pdf. It asked me a password (which raised my hopes for a second) and I entered the password of the certificate, but it didn't work
Did anyone find a solution to this yet?