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BUSINESS GUIDES

How to Add a Purchase Order Number to an Invoice PDF

September 24, 2026

A business customer may receive your invoice, recognise the supplier and still be unable to process it. One common reason is a missing or incorrect purchase order reference. The person approving payment needs to connect the bill with the authorised order and the goods or services received.

Copy the customer's purchase order number into the invoice's PO field, keep your own invoice number separate, and check the billed items against the order. A PO reference helps identify the transaction; it does not automatically prove every charge is approved.

Invoice number and PO number have different jobs

Your invoice number identifies the bill in your records. The purchase order number identifies the customer's order in their records. For example, your invoice might be INV-204 while the customer's PO is PO-7781. Both belong on the same document.

Do not replace your invoice number with the PO number. A single purchase order can sometimes support several deliveries or invoices, so the PO alone may not uniquely identify the bill you are sending.

Check the source before copying the reference

Use the latest authorised purchase order supplied by the customer. Copy letters, numbers and leading zeros carefully. If an email refers to a project code as well as a PO, ask which reference the accounts team needs in each field.

A sales contact's name, a delivery note number and an order number may all be useful, but they are not interchangeable. Put secondary references in Reference or Notes, with a clear label.

Worked example: matching a paper delivery

A customer's PO authorises 20 boxes of paper at USD 24 per box. You deliver and are entitled to bill for 12 boxes now, with the remaining eight to follow.

Invoice fieldEntry
Invoice numberINV-204
Purchase order numberPO-7781
DescriptionA4 copier paper — box of 5 reams — delivery DN-310
Quantity and rate12 boxes × USD 24
Line totalUSD 288 before applicable tax or adjustments

The PO's full order value is USD 480, but that is not automatically the amount of this invoice. The quantity billed must follow the delivery and billing agreement. Keep a separate record showing what has already been invoiced against the order.

A five-point match before you make the PDF

  1. Customer: Check the billing entity and address, which may differ from the delivery location.
  2. Reference: Confirm the PO number and any required line reference.
  3. Description: Use wording the customer can match to the order.
  4. Quantity and price: Check the approved units, rate and amount being billed now.
  5. Supporting record: Retain the delivery note or service approval where relevant.

If the agreed price has changed, get the discrepancy resolved before issuing the invoice. Do not silently substitute a different unit rate and expect the PO reference to explain it.

Prepare the invoice online

The invoice PDF generator includes a Purchase Order Number field and a separate Reference field. Enter the customer's PO in the first and any project or delivery reference in the second. Add the itemised charges and payment details, then generate and save the PDF.

Open the saved file and check the PO number character by character. If the customer gave you a portal, email subject format or attachment requirement, follow those submission instructions as well. Adding a reference to the PDF is only one part of delivering the invoice correctly.

Common questions

What if the customer does not use purchase orders?

Leave the optional PO field blank and use the agreed project or order reference if helpful. Do not invent a PO number.

Can two invoices share one PO number?

They can when the customer's process and billing agreement allow it. Give each invoice its own number and track the cumulative quantity and amount billed.

Will a PO number guarantee payment?

No. The customer may still need delivery confirmation, approval or corrections. Clear references make the invoice easier to process but do not guarantee a payment date.

Create an invoice PDF with your customer's PO reference and check it against the order before sending.

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