Here are some easy ways that can help you solve gpg encryption public key issue.
Don’t suffer from PC errors any longer.
You are defending this error because you do not have the public key of the person who signed the message. gpg should have given you a message with a key id, which is mainly used for signing. Obtain the public key of the man or woman who encrypted the file and place it in your keyring ( gpg2 –import key.