If you just barely installed the application, then the registration window will pop up at the first launch. It will look as you can see in the image attached below. Input your registration name and code then tick ON. However, you will have to buy the program before using this option. The trial version can be used with a maximum of 300 characters of each text file.
Buy program: http://www.xrlly.com/text-to-speech
Proof:
