Hi,
Indicator: Print Operation (1-New) is used for triggering PO message type(PO output type) when PO is created(ME21N) and Print Operation ( 2-change ) is used for triggering PO message type(PO output type) when PO changed (ME22N)) in following path:
SPRO -> MM -> Purchasing > Message -> Output control -> Message Types -> Define message type for Purchase Order -> Fine-Tuned Control: Purchase Order
For Multiple Print of same PO,In General Data TAB select check box of Multiple issuing in following path:
SPRO - > MM - > Purchasing - > Message - > Output control - > Message tyPes - > Define message type for Purchase Order- > Define Message Types for Purchase Order - > Message Type for PO
If you do want changes message type((PO output type)) at all in PO then select check box of CannotBeChanged.
Regards,
Biju K