Lets say in 10 years, 3D printing technology become so advanced, almost anything can be perfectly replicated. So I find some leaked car 3d file, I download it, I print the car. What current laws would I be violating? Civil or criminal? And what future laws can you anticipate?
Patent laws aside, having a printer big enough to print a vehicle or even parts of a vehicle to assemble would not be cheap.
Then you would have to go through the hoops of getting the vehicle certified as road safe to even drive it on public roads.
So having the machinery to print it, the resources to print it, the know how to assemble it, and the procedures to have it certified as road safe, would be enough of a barrier before folks would be concerned with patents.
In the us it isn't too hard to get a title for a kit car. It needs an inspection and emissions test in most states, but it's certainly possible and people do it regularly.
Is it actually illegal to do that for personal use? You can't sale a patented invention without permission from the patent owner but if I go into my workshop and make an exact replica of the newest and greatest anti squirrel wooden bird feeder to hang in my yard have I done anything illegal?
Even if you could print a lot of different materials: A modern car is uncredibly complicated and I'd even take a good enigneer months to fabricate something that does not kill you or others on its first drive. So I guess it won't happen. What I could imagine however is decentralized and more local manufacturing of cars. One company may licence their design, it gets assembled remotely at several places and an engineer has a look before you get it.
In OP's situation where they're downloading a car, I think it's a safe assumption that the car has already been designed/engineered and OP is just printing it out and assembling it. This would be akin to a kit car, and modern kit cars certainly don't require specialized engineering skills to assemble.
I don't think that you would be violating very many, if you kept up to standards, had it tested for roadworthiness and had all the relevant certifications.