Extending Standard Idoc Type

Hi,

I need to extend standard invoice idoc with IDOC type INVOIC01, Message type INVOIC.  When I have checked for the function module or program in WE20 I found the function module IDOC_OUTPUT_INVOIC that triggers the IDoc when the output type is RD00 and Process Code is SD09 .

I tried to debug the idoc through WE19 and also through VF02 but the function module has not been triggered.

I tred searching for the above problem but could not find any appropriate solution. Could you please suggest on how to debug or to trigger the function module so that I can make necessary changes for the extension of IDoc Type.