PAdES specifies the use of CAdES signature formats for signing the PDF content. CAdES builds upon Cryptographic Message Syntax (CMS) and X.509 Public Key Infrastructure, both of which are already supported by Rebex Security.
This means Rebex.Common.dll can be used as the core of a CAdES implementation. Unfortunatey, we don't have a ready-to-use CAdES or PAdES implementation at the moment.