Hi, I'm about to travel tomorrow to Paris from Geneva main station via TGV geneva-Lyon-Paris. Should I still bring some documents like legitimation card, Passport or any? And should I present them before taking the train? It's my first time to travel by train.

Take your passport since you are changing countries. You pass through border control on your way to platforms 7/8 and maybe the police will ask you for it. And also take your permit just in case

And make copies of your documents and leave them in the hands of a good friend. In case you lose the originial documents this is very helpful.