need help in reading .txt file and write it in richtext box in c#

Stream open;
if (openFileDialog1.ShowDialog() == DialogResult.OK)
{
    try
    {
        if ((open = openFileDialog1.OpenFile()) != null)
        {
            open.Close();
            StreamReader r = new StreamReader(openFileDialog1.FileName);
            richTextBox1.Text = r.ReadToEnd();
            r.Close();
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show("Could not read File!" + ex.Message, " Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
    }

}