A Pennsylvania Trailer Bill of Sale is a critical document that can help protect your legal rights. A bill of sale is recommended if you're buying a motor vehicle, boat, or livestock.Trailer registration in Pennsylvania doesn't require a bill of sale, but it's still nice to have one. This form is used to obtain a Pennsylvania Certificate of Title for vehicles not currently titled in Pennsylvania, or which were repossessed (1. The Pennsylvania DMV bill of sale for a motor vehicle, trailer, or boat is a paper account of the essential components surrounding the transaction of a vehicle.