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 then ...

I send you a copy of my padlock, with the hasp open. You lock a box with my padlock and send it back to me. I can open it. The analogy falls down in that you could reverse-engineer a physical key from ...