Bill of Sale and Assignment. Purchase agreements are legally binding contracts used to guide the transition of ownership in a business or the sale of its assets.An asset purchase agreement (APA) is a written legal document that formalizes purchasing a business or substantial commercial asset. An asset purchase agreement is the legal document that will govern the transfer of ownership of a business's assets from the seller to the buyer. THIS AGREEMENT is made and entered into effective the __ day of. Buying or selling a business? Answer a few simple questions to create your own Business Purchase Agreement.