No need to install software, just go to DocHub, and sign up instantly and for free. A Washington purchase agreement documents the sale of a piece of real property for a specified financial figure.First, include the property address as well as its legal description (found on the deed). Then go into detail about what is included or excluded from the sale. If you are using a form, make sure it is current and the right form for your state and area. A purchase and sale agreement is a contract between a buyer and seller for transacting a property in exchange for a specific price.