Read and write Unicode code with richtextbox WindowForm

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace RichTextBox
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            using (var dialog = new SaveFileDialog())
            {
                if (dialog.ShowDialog() == DialogResult.OK && dialog.FileName.Length > 0)
                {
                    dialog.DefaultExt = "txt";
                    dialog.Filter = "Text files (*.txt)|*.txt";
                    richTextBox1.SaveFile(dialog.FileName, RichTextBoxStreamType.UnicodePlainText);
                }
            }
        }

        private void button2_Click(object sender, EventArgs e)
        {
            using (var dialog = new OpenFileDialog())
            {
                if (dialog.ShowDialog() == DialogResult.OK && dialog.FileName.Length > 0)
                {
                    var text = File.ReadAllText(dialog.FileName, Encoding.Unicode);
                    richTextBox1.Text = text;
                }
            }

        }
    }
}