Today, FontCreator utilizes a hybrid license model. The "registration code" is tied to your email address and a hardware ID. If you try to use a stolen code, the software enters "Reduced Functionality Mode," where you cannot export fonts or save projects.
If you have lost your registration code, High-Logic provides a dedicated Registration Code Retrieval tool Requirements
The standard edition ($99) is excellent for hobbyists and small projects. The Pro edition ($199) is worth the upgrade if you need variable fonts or advanced scripting.