Certificate authority questions

Hi all!

Could somebody please help me out and explain following 4 questions

-> What are the main difference between a a self-sign certification implementation and a PKI?
-> What is the difference in the trust model between X500 certificates and openPGP keys?
-> What is the main difference between file encryption and rights management
-> What are the steps followed within an RM Solution, when a file is protected and authorized user attempts access?

Would be really nice to have a explanation to the 4 above

Thanks to all in advance