French people have to file tax returns, it is pre-filled but you still need to check and sign it. It is also the simplest case.

French tax law is actually very complicated, I guess like just about everywhere. If your only revenue is your salary, and you don't have a lot of deductibles, all you need to do is sign the form (electronically). But if you are self-employed, it is highly recommended to hire an accountant if you don't want nasty surprises if you get audited.