Hi Pavan,
You can try putting this command
cmd.exe /C "ren %F %F.pgp"
However I think you cannot use this feature to rename a file in sender file adapter.
The reason being adapter after picking up the file will execute the command which will change the file at OS level. This will not change the filename of the file already picked up. In case this does not work then you need to check the receiver file adapter with following questions
1. Does it suport Dynamic configuration (ASMA) ?
2. Does it support OS command feature?
If you are using SAP SFTP adapter it lacks OS command line feature. Thus only options are to use custom adapter module or add an java mapping code in the scenario. Please check this wonderful blog by Shabarish Vijayakumar. The other helpful articles are
http://wiki.sdn.sap.com/wiki/display/XI/Dynamic+file+name+for+pass-through+scenario
Regards
Anupam