Read the description folks

This does exactly what it says it will in the description. Its only for testing to see if the full version of the app will work with your particular printer setup. The developer is not going to waste your money by selling you an app that doesnt work and since Apple doesnt allow demos, a Lite version is the only alternative. This app worked for me and my printer (shared from the Mac via USB) so I bought the full version.

Gumby_Mac about Printer Pro Lite by Readdle