Hi @Lu Li
Welcome to Microsoft Q&A! Thanks for posting the question.
There are no PGP file encryption/decryption in logic apps. You need to offload this functionality to azure function and call the azure function within logic app.
You need to write your own code for encryption/decryption. I come across this github repro and you can try to explore it and see if it helps you.
Alternatively if you are comfortable with python you can leverage the python-gnupg library.