Before you drive off the lot, be sure to have a copy of the contract and all other documents that you and the dealer have signed. 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.In this guide on how to buy a car in Texas, you'll learn what documents you need, how to get financing, and more for new or used cars. 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. The article includes information about warranties, vehicle title searches, auto insurance, financing, canceling a purchase, and the Texas Lemon Law. Make sure you get a copy of the odometer statement when you sign the contract. Texas law requires you to have liability insurance.