See Also: PKCS1 Members
You shouldn't directly use the PKCS#1 primitives unless you are building your own algorithms based on RSA. Instead you should use the Formatter and Deformatter provided by the framework (which are built using these primitives).
The document "PKCS#1: RSA Cryptography Standard" is available from RSA Laboratories at http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/index.html
PKCS #1 v.2.1 is also published byt the IETF as RFC3447.