Snagit and Camtasia store license information in the registry and/or the local ProgramData folder on the computer. If your account does not have the required permission to write to these locations, the next time the software is started it reverts to an evaluation copy. The workaround is to log in with administrator rights, install the software, and enter your key. During the installation, make sure to select the For All Users option (if available).
- Exit the application completely.
- Right-click the application icon and select Run as Administrator.
- Enter your key when prompted.
See this article for Camtasia for Mac.
See this article for Snagit for Mac.