Smart Converter Pro 3 is for sale on the Apple App store and also on the Shedworx website. The two stores are not linked in anyway.
If you bought Smart Converter Pro 3 on the Apple App store you do not need an activation key. If you're seeing an activation prompt or the demo mode message you have downloaded it from the Shedworx website. Delete that version and go back to the App store and download it from there. If you've already bought it from the App store but downloaded the Shedworx version for VOB file support please see our FAQ on VOB files.
If you've purchased Smart Converter Pro 3 from the Shedworx website you should have received an activation key shortly after your purchase. If you didn't receive your activation key please check your spam/junk folder. If it is not in there contact support and let us know and provide the email address you used for your purchase so we can look up your key.