An asset purchase agreement (APA) is a written legal document that formalizes purchasing a business or substantial commercial asset. Purchase agreements are legally binding contracts used to guide the transition of ownership in a business or the sale of its assets.A business sale agreement is a legal document that describes and records the price and other details when a business owner sells the business. 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. A Texas Business Purchase Agreement will help transfer business ownership and outline the terms of the sale.