How can I create a simple software like KD Authorpreneur?

KD Authorpreneur
I want to create a simple 'fill in the blanks' software that generates a *.txt
(or pdf, html) as result.

A step by step process that creates a *.txt file in the end with for
instance a complete sales letter, or email template, or some kind of copy.

Any suggestions? I dont know nothing about coding.