The certificate issued by Edx is signed by a gpg key so that it can be validated independently by anyone who has the edX public key. For independent verification edX uses what is called a "detached signature" meaning that the signature for the certificate is contained in a separate file with a ".sig" extension.

To complete the verification procedure you will need the following three files:

Ensure you have the pdf, the ".sig" signature file and the edX public key copied to a single directory before you begin.

Import the edX public key on OSX using GPG Keychain

Import the edX public key on Microsoft Windows using gpg4win

Verify the edX certificate using gpg on both OSX and Windows