What document is used to authorize the purchase of supplies or services?

The Purchase Order is the correct answer because it serves as a formal document that authorizes the purchase of goods or services. This document specifies the details of the transaction, including quantities, prices, and delivery information, which facilitates clear communication between the buyer and seller. By issuing a Purchase Order, organizations ensure they have documented the purchase agreement, which can be referenced for contract terms and compliance. This also helps to manage and control spending within budgetary constraints.

The other options, while related to the procurement process, do not serve the same function. The Supply Requisition is an internal request for supplies and does not authorize a purchase on its own. A Procurement Notice generally provides information about upcoming procurement opportunities but does not serve as an authorization document. A Contract Agreement is a broader legal document that may encompass multiple Purchase Orders but operates at a different level than a Purchase Order itself, often outlining terms for longer-term supplier relationships rather than individual purchases.