void Main()
{
    var psi = new ProcessStartInfo();
    psi.FileName = "cmd.exe";
    psi.Arguments = "/c start /ABOVENORMAL notepad \"c:\\abc.txt\"";
    psi.CreateNoWindow = true;
    psi.UseShellExecute = false;
    psi.RedirectStandardOutput = true;
    Process.Start(psi);
}