Use the types Process and ProcessStartInfo setting
ProcessStartInfo.UseShellExecute[
^] to true. Then if you set ProcessStartInfo.FileName to the PDF (full path) and the ProcessStartInfo.Verb to something like "open". Create a Process and invoke the Start method with th ProcessStartInfo as a parameter.
If the PDF reader is still associated with the extension PDF this will open the PDF reader with said document.
Best Regars,
-MRB