Is there a shelf app to populate a template letter?

I visit clients and after each visit i need to send them a pdf letter. Searched for a solution but found none. I need something that will allow me to enter in some text boxes and that information to populate the letter. Like name, date, address, value. It must then send the letter on pdf format to the client. Does such a thing exist – needs to be something i can do from my phone so an app like interface