A Pennsylvania vehicle bill of sale is a legal document formalizing the sale and purchase of a motor vehicle between a buyer and seller. When selling a vehicle, the seller must sign and handprint their name on the proof of ownership document.How to fill out the Pennsylvania Motor Vehicle Bill of Sale Form? 1. Write the vehicle details such as make, model, year, and VIN. 2. Vehicle Registration Forms. A Pennsylvania bill of sale documents the transfer of ownership of a motor vehicle, boat, gun, or other valuable asset.