SAP: difference between Purchase Order (PO) and Purchasing Document

A Purchase Order is a document type that is a formal request for materials or services from an outside vendor or plant.

In the SAP System, the different kinds of purchasing document are distinguished from one another by means of the document type. The Document type determines the relevant number range and the fields that are offered to you for data maintenance purpose.

Document types are defined for RFQs, purchase orders, and contracts, for example. The standard SAP system includes certain document types.

The following purchasing document types can exist for the purchasing document category purchase order,for instance:

Standard purchase order -NB
Stock transport order  UB
Framework order  FO