If you want to run Zorin OS Pro from a USB stick (portable), you have two distinct methods depending on your needs.
If you are a student or teacher, email Zorin support directly. They have been known to provide complimentary Pro keys (actual download links) to educational institutions. Note: They will ask for a .edu email address. zorin os pro key portable
Zorin OS frequently runs "Pay What You Want" promotions (typically around Black Friday, Christmas, or the release of a major version like Zorin OS 17). During these periods, you can legally download the Pro ISO for as little as €0.01. Set a calendar reminder. It is far safer than downloading malware. If you want to run Zorin OS Pro