Item Code Display on Purchase Orders
The item codes that appear on PO PDFs are vendor product codes. If you would like to add your item codes to PO printouts in addition to the vendor codes, turn on the option Admin -> Payables -> General Setup -> PO -> Show Internal Item Code On PO.
You can add or modify vendor product codes by going to Inventory -> Items -> Items by Vendor, or by going to Inventory -> Items, selecting an item, and then clicking the Item Vendor Add/Edit button at the top of the page. Put the vendor's item code in the Vendor Product Code box. This vendor code will then be displayed on purchase orders.