VF01 -Save -Generate a text file

Hi Experts ,

I have a requirement where in VF01 when we save a billing document a text file has to be generated and dropped on a server .

I am using standard IDOC type INVOIC defined a port in WE21 , the file gets saved on a directory but the Idoc file has lot of information.

Is there any way we can format the Idoc file so that it has the information in below format .

Billing doc -12345

Shiptoparty - xyz

Date:21.07.2017

Or is there any way we can generate a text file with invoice details after VF01 SAVE . some user exit may be ?

Thanks