If you have a PGP public key, you can open it with NotePad, and it will look something like:

-----BEGIN PGP PUBLIC KEY BLOCK-----
Version: PGP Desktop 10.0.3 (Build 1)

mQGiBDpvus8RBAD6wy3t64YUrCxAQXolXPmxpeg9RTBjEApmOW+1PkZqGJCRJ91o
qToUwMD/nTlDNLRgjjZY+sAh6JJMnaYZacVH9WaL7BpVVWDSqYP3okJxeVhAqTUi

{many more lines something like the two above}

-----END PGP PUBLIC KEY BLOCK-----

It sounds like you have such a public key and want to import it to a recent or current version of PGP Desktop?

If this is what you have, while opened in NotePad, you can click on the PGPtray icon in the Windows notification area, and select Current Window - Decrypt and Verify to import the key. 

If you have the exported key in a file with an asc extension, you can either double click on it, or right click and select PGP Desktop - Import Keys.