Why don't you use activation codes that turn the trial version into a full version?
We do not work with activation codes because you can find them very easily on the internet. Typically software manufacturers protect against this problem using online activation, but this would make customer dependent on the availability of our activation servers and an internet connection.
We are working with separate trial and full versions instead, where the full version is not freely available for download and must be installed over the trial version. After purchasing our software, customers get an account for our customer area where they can download the full version for at least 12 months. Our customers will also receive a personalized installation key, with which they can install the full version. Login data and key should be stored in a safe place. Installing the full version over the trial version will preserve your existing data and settings.