PhotoKey Pro includes a 3-seat license, which allows the software to be installed and used on up to three computers simultaneously.  If you have a small photography business, for example, the Pro license allows you to have up to three people running the software simultaneously on different computers.

The installers for all your registered software are permanently stored in your account, so you can download them any time, as many times, and as often as you need to: https://fxhome.com/account

Reinstalling the software, or moving an installation from one computer to another is perfectly fine, provided that it is not installed simultaneously on more computers than the license allows. 

Legacy versions of PhotoKey, including the versions of PhotoKey Standard and PhotoKey Lite, feature a single-seat license, and can only be installed on a single computer at a time. If you wish to move a standard or lite license of the software to a new computer, you will first need to delete it from the computer it is currently installed on.