To add a PCMark 10 Advanced Edition license key to Steam, first create an account on 3dmark.com or log in to your existing account. If your 3dmark.com account does not have a Steam sign-in associated with it, you need to add the Steam sign-in method to your account before you can add your license key. Next, go the Settings page, add your license key in the box under ADD PCMARK 10 TO YOUR STEAM LIBRARY, and then click on the SUBMIT button. This action can be performed only once for a license key.
Please note that it is not possible to activate Professional Edition licenses on Steam.