A form for my own use which creates a document?

[CactusWren]

I create invoices and contracts where everything is the same except for name, date, etc. I want to be able to make it so I can just enter in these new fields and maybe tab through, instead of manually selecting the text and writing over it each time. I didn't even know what this process is called so headed over here in hopes of being pointed in the right direction. Thanks!