OpenFileDialogBox in Winform (C#))

OpenFileDialog openFileDialog1 = new OpenFileDialog();

            openFileDialog1.Title = "Attach Document file (PDF)";

            openFileDialog1.CheckFileExists = true;
            openFileDialog1.CheckPathExists = true;

            openFileDialog1.DefaultExt = "txt";
            openFileDialog1.Filter = "PDF file (*.pdf)|*.pdf";
            openFileDialog1.FilterIndex = 2;
            openFileDialog1.RestoreDirectory = true;

            openFileDialog1.ReadOnlyChecked = true;
            openFileDialog1.ShowReadOnly = true;

            if (openFileDialog1.ShowDialog() == DialogResult.OK)
            {
                txtFileAddress.Text = openFileDialog1.FileName;
            }