A PAC code doesn't exist a PAC does.
Note: PAC = Port Authorisation Code.
Therefore PAC Code = Port Authorisation Code Code.
When you request a PAC from your current provider they will issue you with a code, this you give to your new provider and allows you to take (port) your number to the new network.
An unlock code is a code you enter into your phone to remove the network lock, and allow you to use any networks SIM in your phone.