How to: Enter External Document Numbers
You can enter external document numbers for customers and vendors in all sales and purchase orders, invoices, and credit memos. You can use these numbers to search for posted sales and purchase lines later.
To enter external document numbers in sales and purchase orders
In the Search box, enter Sales Orders or Purchase Orders, and then choose the related link.
Select a relevant sales order or purchase order. On the Home tab, choose Edit.
On the General FastTab, in the External Document No. field or the Vendor Invoice No. field, enter the invoice number.
Enter information into the required fields.
Choose the OK button.