Autocomplete any character in textbox

Do you maybe just need to look at a working example?

private void Form1_Load(object sender, EventArgs e)
{
    // Create the list to use as the custom source.  
    var source = new AutoCompleteStringCollection();
    source.AddRange(new string[]
                    {
                        "January",
                        "February",
                        "March",
                        "April",
                        "May",
                        "June",
                        "July",
                        "August",
                        "September",
                        "October",
                        "November",
                        "December"
                    });

    // Create and initialize the text box. 
    var textBox = new TextBox
                  {
                      AutoCompleteCustomSource = source,
                      AutoCompleteMode = 
                          AutoCompleteMode.SuggestAppend,
                      AutoCompleteSource =
                          AutoCompleteSource.CustomSource,
                      Location = new Point(20, 20),
                      Width = ClientRectangle.Width - 40,
                      Visible = true
                  };

    // Add the text box to the form.
    Controls.Add(textBox);
}

(Example lifted from here.)