If you or your organization previously purchased a license for ProPresenter 6, you don't need to buy it again. You can recover your existing "Unlock Code" by using the official ProPresenter Information Center
ProPresenter 6 is a legacy version of Renewed Vision's professional presentation software. While there are no legitimate ways to obtain a permanent "registration code" for free, there are several official methods to use the software at no cost or recover a code you already own.