If the car was registered before 2014, you will receive the old registration papers together with a temporary document number. You can use this to transfer the car at the post office. You will immediately receive a part of the new registration code. You will receive the other part of the registration code with the new registration card by mail. The "old" registration papers will be cancelled.
Note: it is important that you carefully keep both parts of the registration code. The registration card serves as an ID card for the car and must be able to be shown when you are driving the car.