How to Open Text files into textbox in C# Vsual Studio

Open Text files in C# 

1-Add one Button & RichTextBox from toolbox
Now add the yellow highlighted namespace as follows.

using System.IO;

namespace WindowsFormsApp1
{
    public partial class Form1: Form
    {
        public Form1()
        {
            InitializeComponent();
        }
Now go to the button1_click event and copy the yellow highlighted code.         private void button1_Click(object sender, EventArgs e)
        {
            Stream stm;
            OpenFileDialog ofd = new OpenFileDialog();
            if (ofd.ShowDialog() == System.Windows.Forms.DialogResult.OK)
            {
                if ((stm = ofd.OpenFile()) != null)
                {
                    string str = ofd.FileName;
                    string ftxt = File.ReadAllText(str);
                    textbox1.Text = ftxt;
                }
            }

        }