Depends on how you've stored it, The actual file in the container or just a reference to it. With store by reference, you can just double-click the field. With the actual file stored, you can use export field contents to open it. (You can even export the file to the temporary items folder to avoid a build up of exported files on the client computer.)
Just for a little more info to round it out, you can also check out the "SendEvent" script step.
It is no better an option, just another one...
Check out this old thread...I am assuming that this approach still works on FMP11, I have not tested it myself.