The full and trial versions of PerfectIt are identical. However, the trial is time limited so that you cannot use it when the trial is over. So when you purchase, you should use your license key to unlock the trial.
You can get the full version of PerfectIt here. When you launch PerfectIt, it will prompt for your registration details. At that point, please copy and paste the license key and details that were sent to you when you purchased the software into the registration form. If you need to get the details again, they're available here.