Formatting ToShortDateString to dd/MM/yyyy
ToShortDateString does not have an overload which takes any parameter.
If your ToShortDateString() returns MM/dd/yyyy format, that means your CurrentCulture has this format in it's ShortDatePattern property.
You can always use custom formatting for that like with proper culture like;
TextBox2.Text = DateTime.Today.ToString("dd/MM/yyyy", CultureInfo.InvariantCulture);