You can view PO Related Documents when you open a purchase order and click the Related Documents button. You must have View Invoices and POs/BPOs permission added to your role to view related documents.
If an order has been novated (a change in vendor), the original vendor has access to Related Documents up to the point of the novation. The new vendor has access to the Related Documents from the time of the novation.
To view PO Related Documents: