Jerry, the possible problem which I can see with this is related to file extension association which is done in the registry.
If you want to get the file name as a part of program arguments, this should be specified while doing the association as %1.
Attached is the sample .reg file inside zip to set this association. Edit this file and provide proper path of your .abc file handler in place of dummy path which is C:\\PATH_OF_ABC_HANDLER\\ABC_HANDLER.exe
You should be able to get the file name as a part of program argument. This will work now.
Thanks
Amit
http://www.eggheadcafe.com/fileupload/-1052171516_abc.zip
The .reg file is inline below as well ::
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\.abc]
@="ABC"
[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\.abc\shell]
@="Open"
[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\.abc\shell\open]
[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\.abc\shell\open\command]
@="C:\\PATH_OF_ABC_HANDLER\\ABC_HANDLER.exe \"%1\""