Individual purchase orders are used when your customer orders goods from you that are not in stock and must be ordered from one or more external vendors.
During sales order entry, the system automatically creates a purchase requisition item. The purchasing department creates a purchase order based on the requisition and the vendor ships the goods directly to you (unlikethird party order processing, where the vendor ships directly to your customer). You then ship the goods to your customer. While the goods are part of your inventory, you manage them as part of the sales order stock. Sales order stock consists of stock that is assigned to specific sales orders and cannot be used for other purposes. For more information, see Make-To-Order Production.
The processing of individual purchase orders is controlled by the material type. Material types define whether a material is produced only internally, can be ordered only from third-party vendors, or whether both are possible. For example, a material that is defined as a trading good can only be ordered from a third-party vendor. However, it might be advantageous at times to procure products that are normally produced internally (such as finished goods) from an external vendor.
You can track costs and revenues for individual purchase orders in the same way as you track costs for make-to-order production. The material in question must be maintained for the MRP group 0020 and a plant must be assigned at the item level in the sales order.
Materials Management documentation for Purchasing.