How to create textbox and set variable

Hello there,
I made an istaller and i got new challange that, i want to read a text file, find and replace some word from the text file. The idea is that installer will prompt a window with a text box and ask from the user with what they want to replace with!

For example:
I have "ContractorID" in text file an want to replace that with a number.

You might find some help on the Wiki:


(Here's one example and here's another.)

Thanks. Anyone can give me more details.