private void SendToPrinter()
{
   ProcessStartInfo info = new ProcessStartInfo();
   info.Verb = "print";
   info.FileName = @"c:\output.pdf";
   info.CreateNoWindow = true;
   info.WindowStyle = ProcessWindowStyle.Hidden;

   Process p = new Process();
   p.StartInfo = info;
   p.Start();

   p.WaitForInputIdle();
   System.Threading.Thread.Sleep(3000);
   if (false == p.CloseMainWindow())
      p.Kill();
}