Hi! There are many people in the USA, who import cars from Europe, especially from Germany, and that's why it is easy to perform. So, there are not a lot of documents required: the vehicle needs to have a VIN or, if not, then the PIN; an EPA declaration form and CBP declaration form. Check the full list here https://help.cbp.gov/app/answers/detail/a_id/218/~/requirements-for-importing-a-vehicle-%2F-vehicle-parts