A purchase order is a document you send a supplier stating what you are buying, and it has a life afterwards that most descriptions skip. It is raised, approved, issued, then received against as deliveries arrive, invoiced against as bills come in, and eventually closed. The middle two stages are where the work is and where most problems start.
Raised, approved, issued
Somebody states what is needed with quantities and prices, a unique number is issued automatically, and the order is approved before the supplier is told, because the commitment exists once they act on it. It is then sent, and the sending is recorded, which answers whether the supplier ever received it when a delivery goes missing.
Received against, over time
Deliveries rarely match orders exactly. Part shipments, substitutions and over-deliveries are normal, so each line carries an ordered quantity and a received quantity that diverge for weeks. Recording receipts at line level as they happen is what makes the invoice checkable and what produces the accrual at period end without anybody rebuilding it.
Invoiced against, then closed
Invoices arrive quoting the order number and are matched against the order and the receipts. The order is closed when received and invoiced quantities reconcile with ordered, or when somebody decides the balance will never arrive and records why. Orders left open forever inflate commitments and make the open-order report untrusted.
Questions people ask about how do purchase orders work
Can one order produce several invoices?
Yes, commonly, for staged deliveries or ongoing services. That is why line-level matching with running quantities matters.
Who closes an order?
Usually purchasing, reviewing anything open beyond its expected lead time. Leaving closure to nobody degrades the report everybody relies on.
What about services with no delivery?
The receipt becomes a confirmation that the work was done by whoever commissioned it, and the order behaves the same way otherwise.
How long should an order stay open?
No longer than its expected lead time plus a margin. Reviewing anything older weekly, and closing what will not arrive with a reason recorded, is what keeps the open-order report worth reading.
Do suppliers need to acknowledge orders?
It is useful rather than essential. Knowing an order was received removes a class of dispute, and it matters far less than tracking what actually arrives against it.