convert Windows Server 2012 Std Eval to Standard
to convert your evaluation edition of Windows Server 2012 Standard to a full Standard verison with a product key use the following command:
dism /online /Set-Edition:ServerStandard /ProductKey:XXXX-XXXX-XXXX-XXXX-XXXX /AcceptEula
This will convert your evaluation edition to a full activated version - using the product key in the command. A restart is required after this command is executed.