From purchase order to invoice: the documents of a sale explained

A sale between two businesses rarely involves a single document. The buyer orders, the seller confirms, the goods are packed and delivered, and only then is the invoice sent. Each step has its own document. Knowing who issues which one, and when, avoids disputes and makes every payment easier to match.

The usual order of documents

1. Request for quotation (RFQ): the buyer asks suppliers to price a list of items.
2. Quote: the seller answers with prices and a validity date.
3. Purchase order (PO): the buyer confirms what they want to buy, at what price and by when.
4. Sales order: the seller confirms the order internally and to the customer.
5. Packing slip and delivery note: they travel with the goods; the customer signs the delivery note on receipt.
6. Invoice: the seller asks for payment, quoting the PO number.
7. Receipt: the seller confirms payment.

Small businesses often skip some steps, but the PO, the delivery note and the invoice are the backbone of most sales.

Purchase order vs sales order

Atlas Studio12 Harbour Street
Casablanca 20250[email protected]

Purchase Order

Number

PO-0042

Date

Mar 14, 2026

Vendor

Northwind Trading48 Rue de Lyon
75012 Paris

Ship to

Northwind Warehouse9 Quai de Bercy
75012 Paris

Description	Qty	Unit price	Amount
Brand identity design	1	$1,800.00	$1,800.00
Website pages (5)	5	$320.00	$1,600.00
Product photography, half day	1	$650.00	$650.00
Print-ready files	1	$150.00	$150.00

Notes

Thank you for your business.

Subtotal	$4,200.00
Tax 20%	$840.00
Total	$5,040.00

Why the PO number matters

Many companies cannot pay an invoice that does not quote their purchase order number, because their accounts team matches three documents: the PO, the delivery note and the invoice. If the three agree on items, quantities and prices, payment is approved. If they do not, the invoice waits. Always copy the PO number into the "PO number" field of your invoice.

Packing slip vs delivery note

A packing slip lists what is inside the parcel, usually without prices, so the receiver can check the contents. A delivery note is signed by the customer to confirm the goods arrived in good condition. Some businesses use one document for both purposes.

Create the documents you need

All these documents share the same customer and items, so you only type them once. Create a purchase order, or open a sales order and choose "Convert to" to produce the packing slip, delivery note and invoice. Read more about the step before the order in quote vs estimate.