You have to use file stream to convert byte array to file
byte[] yResult ;
string strFileName ;
if (yResult.Length > 0)
{
FileStream fs = File.Create(System.IO.Path.GetTempPath() + "\\" + strFileName, yResult.Length, FileOptions.None);
fs.Write(yResult, 0, yResult.Length);
fs.Close();
fs = null;
ProcessStartInfo pf = new ProcessStartInfo(System.IO.Path.GetTempPath() + "\\" + strFileName);
Process.Start(pf);
}