What is a document that shows proof of purchase?

A receipt is indeed the correct answer because it serves as a formal acknowledgment of a transaction between a buyer and a seller. It typically includes details such as the date of purchase, items purchased, quantities, prices, the total amount paid, and the method of payment. A receipt acts as proof that the transaction occurred, confirming that the buyer has paid for the goods or services.

In contrast, while an invoice can also serve as a record of a transaction, it is primarily a request for payment and does not necessarily confirm that payment has been made. A statement typically summarizes account activities over a period and may not pertain to a specific transaction. A bill indicates an amount owed and may not serve as proof that the customer has already paid. Thus, the characteristics of a receipt make it the definitive proof of purchase.