Create Purchase Order from Part Profile
Purchase Orders can be created directly for a specific part from the Part Profile page (in addition to creating POs for multiple parts as shown in the Purchase Orders Overview article).
When you're viewing an individual part, click the Add to PO link in the Locations panel.
On the Add to Purchase Order screen, enter the Quantity and then either select an existing PO or create a New Purchase Order.
NOTE: Only existing Purchase Orders at the same Part Location will be available for Add.