Thankyou so much!! I've been looking through your riddle game and I haven't got very far yet but it looks really cool :) For getting plain text into files there's a number of good ways to do it. It can be as simple as just opening the image in a text editor and writing it in (but normally it would have to be after the bytes which mark the end of the file otherwise it might not open correctly)

or, if you're on Linux you can put your .txt file in a zip folder and then append the zip to the image file using the ">" operator (credit to Dawnvoid for teaching me that one)