Final answer:
The document that notifies the purchaser of their obligation to pay is the vendor invoice.
Step-by-step explanation:
The document that notifies the purchaser of his or her obligation to pay is the (B) vendor invoice. A vendor invoice is a statement of the goods or services provided by the vendor and a request for payment. The invoice will typically list the products or services, their costs, the total amount due, and the payment terms. On the other hand, a receiving report documents the receipt of goods from the vendor, an acceptance report confirms that the goods or services meet the required specifications, and a vendor packing slip lists the contents of a shipment.