Blank Purchase Agreement
In legal terms, a contract is any agreement between parties to exchange things of value, such as goods and services for cash. A simple handshake agreement is legally binding, but its terms are not always provable if a dispute arises. However, you don't necessarily need pages upon pages of legalese. A basic contract agreement often works best for a simple business transaction.
Only some places where these treaties and agreements are republished are considered "official" and having a binding version of that agreement. So, even if you find a republished version through Google, that may not mean it is a binding replication of the text. Frequently, they are published officially online through particular websites sponsored by the international organization(s) that created the agreement.