After buying the product, a Serial Number is sent to the customer. It is the 'proof of purchase' and it is unique. If it is created using the Activation Server 4 it will always have this format

 

 dO8uc-G1iC9-jOGeA-BqgEX-U71lD-0V1VX

 

There are 6 blocks each with 5 characters. The blocks are separated by a hyphen for better readability.

 

You can alternatively use your own Serial Number Keys or IDs.