You don't require specific set ups in Purchasing Unless you need the PO
to be created Automatically
Make sure following steps
Order management
1.Create sales order with type:
Dropshipment (Make sure
Order lines has source type:
External)
Once order is booked.Run "workflow background " Process with
source;Order Entry
Or Run Purchase release
Purchasing
3.Run Requisition Import
4.PR will be created after step3
5.Depending on the set up (whether automatic document creation =Yes or
No)
PO will be created(Check the shipment Destination org;its the Customer
address rather than Inventory org)