My bank wants purchase agreement or bill of sale before sending out a check to the dealer. A Pennsylvania vehicle bill of sale is a legal document formalizing the sale and purchase of a motor vehicle between a buyer and seller.Enter total purchase price in Section I, including installation charges on contract sales of mobile homes. Watch this before you finance your next car (former dealer explains how to read a purchase contract) I am a resident of another state. The final hurdle you face is signing the vehicle purchase agreement; a confusing and convoluted document that we explain in detail here.