Hi Chetan,
PORDCH is an inbound IDOC & ORDCHG outbound IDOC.
For cases, where you can use these, please go through below links.
http://scn.sap.com/message/5972631
http://help.sap.com/erp2005_ehp_04/helpdata/en/fa/461898e451c148921d615bad11fd48/content.htm
http://scn.sap.com/thread/1311543
Rgds
Sourabh