Also Google for "java exec rundll32". You give this technique a filename and it goes through the same mechanism Windows goes through to open a file when you double click on it. That is, if MS Word is the default application for extension "doc" it will open Word. Be aware it might fire up Open Office or some other app if the user has associated the extension differently. That might be a good thing or a bad thing depending on your requirements.
To see RUNDLL32 work without Java, open a command window and type the fully qualified name of your Word doc as a command. It ought to open right up. Try that with different extensions or a URL like "http://www.javaranch.com"
A good question is never answered. It is not a bolt to be tightened into place but a seed to be planted and to bear more seed toward the hope of greening the landscape of the idea. John Ciardi
You could also look at Java Desktop Integration Components. I've never tried it, but it appears to have functionality for opening files with the registered application. Great if you don't know if the user has Word or OpenOffice.