For .com, .net, .org, .info, .biz ect
The Domain AuthCode is also known as the Domain Authorization Code or EPP Code. It is a 6 to 16 character code assigned to your domain name. This code is assigned by your registrar and is simply a password for your domain name. The password is used as a security and authorization measure in events such as a domain transfer.
When you initiate a transfer registrar request, the registry will send you a transfer authorization request. You need to reply to the authorization request with your Domain AuthCode. Only transfer authorizations received with the correct Domain AuthCode will be approved.
For .PK Domains
The .PK domain does not contain the Authorization or EPP Code to transfer it from one registrar to another. There is a Standard Procedure defined by PKNIC for the Domain Name Transfer which is available on http://pknic.net.pk/change-registrar.html.