>Think you'll have to dig in the registry to find the open command
>
>(1) under HKEY_CLASSES_ROOT look for dot + extension
>
>eg pdf becomes .pdf
>
>The (default) on the right gives you the name of the application
>
>(2) under HKEY_CLASSES_ROOT\nameOfApplication\Shell\Open\Command you will find the command line
>
>See attached example

Thanks, I'll go this route, but it's quite inconvenient, don't you think? I remember it used to be available to see and change directly from the Windows File Extensions dialog.