Simply install Foxit PDF Editor on your macOS device, you'll then enter the Free Trial Mode after you run the application for the first time.
Then please go to the Help Tab and select "Activate".
IT Admins and Deployment:
Please use the Foxit macOS Customization Tool to create a new PKG with the key embedded. If you'd prefer a scripted deployment, the license key is stored under "~Library/Application Support/Foxit Software/Foxit PDF Editor/Licenses"