Have you tried making a tabletop RPG? Or some other type of game that only requires a PDF?
I'm talking about an "analog game." As in, a board game. Like Candyland. Or a table-top Role Playing Game. Dungeons & Dragons, if you will.
Basically, you write the rules, and players who've downloaded your document read them and follow them to play the game.
For example, I released Sage Journey: Disc 2, a game where you print it out and follow my instructions for how to proceed in the adventure and fight monsters. <https://neuronbureau.itch.io/sage-journey-disc-2>.
But you don't have to make an RPG. Yahtzee is simply a game where you roll dice and count up numbers. Sorry! is just rolling dice and moving around a board. Poker cards are used in different permutations of playing 1 card on your turn.
You can use any word processor to make them, then upload the file to itch. And if you want to read PDFs for free, you can probably view them in any browser, most notably Google Chrome.
I have Microsoft Word, so I can convert my files to PDF for free. But OpenOffice and LibreOffice are free and should also be able to do it. Or, you can write it in HTML5, if you want.