HMP - How do I activate HitmanPro?

You first need to install HitmanPro, see FAQ1.

Do not activate a new product key if you still have remaining days on an active existing license. Remaining days on an older active license will not be added to the new license.

Open HitmanPro
Click on Settings in the bottom left corner
Go to the License tab
Enter your product key, including hyphens
Click Activate
Your license is now successfully activated on your computer