Xceed Encryption library does not support PGP. This request is on our feature request list. However, there is no time frame nor guarantee that this feature will be added in the future.
But, it is feasible to produce a file format which is PGP compatible with our library. However, we have never try it ourselves. Xceed Encryption is more of a low level library than an applicative library, like Xceed Zip for example, that directly support the Zip file format.