1 If you're financing your purchase ; 3 The actual vehicle purchase agreement ; 4 Buyer's trade in certification ; 5 Warranty disclaimer and documentary fee notice. You'll need to sign the car purchase agreement (or dealer bill of sale), the title, an odometer statement, and sometimes a damage disclosure statement.Watch this before you finance your next car (former dealer explains how to read a purchase contract) How to fill out the Motor Vehicle Purchase Agreement Instructions? Here are six of the most important documents you'll be asked to sign when you're making a deal on a car. We'll also point out which section matters most. Information you can expect to fill out includes the car's VIN, make, and model, the name and permanent address of each party involved, and the sales amount. Vehicle forms: Application for Texas Title (130-U), Application for Motor Vehicle Title, Service and Runner License.