I've been looking around the internet for an example that shows how to encrypt a file with an existing PGP public key that was sent to me. The examples I find generate the key pair on the fly and ...

In PGP systems, users each have a set of two keys. One is public any may be shared with anyone that wants to send data to the user, and the other is private and is used only to decrypt sent data.

The EFF has chimed in on this exploit and advises everyone to immediately disable and uninstall tools that automatically decrypt PGP-encrypted email.