This snip opens any kind of document (e.g. .PDF, .DOC, .C, .HTM, etc.) using the default application associated with it. This relies on starting a new process with the .UseShellExecute property set to true.
The main overloaded function OpenDoc(filename) will open any associated document using the default OPEN verb. If you are trying to edit a file, for example, a command file, then you need should call OpenDoc with the "EDIT" verb. Some associations also a "PRINT" verb.
Since the return result is a System.Diagnostics.Process object, you can also monitor or kill the process.
System.Diagnostics.Process doc = OpenDoc("C:\\WebPage.htm");