If you wish to access the premium features or support the developer, you should only obtain a key through official channels.
This is a premium variant offered by the developer as a way to fund the project. While the core source code is identical to the free version, the Ultimate version includes additional plugins and skins. How to Get an Official Ultracopier Product Key ultracopier product key
Licenses can be bought from the official shop. Prices for the Ultimate version have historically been around $15.00 . If you wish to access the premium features
Searching for a "free" or "cracked" Ultracopier product key on third-party sites poses significant risks: Ultracopier/ProductKey.cpp at master - GitHub ultracopier product key
Understanding the Ultracopier Product Key: Free vs. Ultimate Edition