Posting Documents: Introductory Comments
Documents are posted at the end of the validation process or at the end of the workflow.
When a document is posted, the following steps are executed:
The document contains the document status
(completed).The document can be displayed but can no longer be processed.
The confirmation items of all PO items are written to the respective SAP purchase orders:

Notice
A document may relate to a single SAP purchase order or to multiple SAP purchase orders. The items of a document are distributed to match the items of the respective SAP purchase orders. That means that SAP purchase orders are not created during the confirmation process.
The attachments to the document are linked to the SAP purchase orders.