Изменить заголовок окна

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        static extern IntPtr GetForegroundWindow();
 
        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        static extern int GetWindowText(IntPtr hWnd, StringBuilder text, int count);
 
        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        static extern int GetWindowTextLength(IntPtr hWnd);
 
        private string GetCaptionOfActiveWindow()
        {
            var strTitle = string.Empty;
            var handle = GetForegroundWindow();
            // Obtain the length of the text   
            var intLength = GetWindowTextLength(handle) + 1;
            var stringBuilder = new StringBuilder(intLength);
            if (GetWindowText(handle, stringBuilder, intLength) > 0)
            {
                strTitle = stringBuilder.ToString();
            }
            return strTitle;
        }

private void tmr_update_Tick(object sender, EventArgs e)
        {
             txtResultTitle.Text = GetCaptionOfActiveWindow(); 
        }