you can generate Receipt without Purchase order , the first option is "Automatic receipt" ,in this functionality system would link the receipt with system generated PO (you need not create PO manually).
Automatic receipt functionality generally work with "Full VMI (Customer Side)" or "Item Subcontracting" or if you have some specific scenario than share with me i would try to map with this functionality.
Note:- "Automatic Receipt " functionality facilitate you to receive inventory automatically without creating PO manually so it doesn't mean that you can receive inventory without any Purchase Order because in this functionality as well system link PO(system generated) with receipt.
Other than above solution we have another option of "generate Order for Unexpected warehouse receipt " in which LN automatically creates a purchase order against which the items are received for the purchase business partner.
In this option as well system would generate Purchase order for unexpected receipt.
Last edited by chandrajeet : 3rd July 2017 at 14:18.