This is not a realistic scenario whatsoever. Printers tend to print fonts pretty accurately to their on screen presentation. Even using contextual alternates, t

This is not a realistic scenario whatsoever. Printers tend to print fonts pretty accurately to their on screen presentation. Even using contextual alternates, the perpetrator would have to change the font before printing. But if the perpetrator has this opportunity, they do need the font at all, they can just change the content. For example, CSS media queries that I mentioned in the other comment can show one paragraph on the screen and another when printing. You don't even need to put both in the HTML - CSS ::before and ::after will happily do that for you. It's also not very wise in general to not read the final printed version of the contract before signing