You could use Process.Start(<file path>) to open the default application for that file type. That will open the default PDF viewer in your case. You could use Process.Start("iexplore", <file path>) to (try to) open any file in Internet Explorer. If you want to ensure you use the default browser, I believe you will have to delve into the registry to determine what it is. I have read that there is a section in the registry that keeps a list of installed browsers and e-mail clients and which is the default, but I can't remember the details. A search on the Microsoft web site should turn it up if that's what you need.