浏览器使用c#在windows窗体应用程序

我在Windows窗体应用程序中使用c#开发了一个浏览器，现在我想在文本文档中放置一个按钮来存储HTML代码，我该怎么做呢，谢谢

namespace browser
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private void button3_Click(object sender, EventArgs e)
        {
            browser.Refresh();
        }
        private void home_Click(object sender, EventArgs e)
        {
            browser.GoHome(); 
        }
        private void back_Click(object sender, EventArgs e)
        {
            if (browser.CanGoBack)
            {
                browser.GoBack();
            }
        }
        private void forward_Click(object sender, EventArgs e)
        {
            if (browser.CanGoForward)
            {
                browser.GoForward();
            }
        }
        private void stop_Click(object sender, EventArgs e)
        {
            browser.Stop();
        }
        private void go_Click(object sender, EventArgs e)
        {
            string url = textBox.Text.Trim();
            browser.Navigate(url);
        }
    }
}

using System.Net;
using System.Net.Http; 
WebRequest req = HttpWebRequest.Create("http://yourwebsite.com");
req.Method = "GET";
string source;
using (StreamReader reader = new StreamReader(req.GetResponse().GetResponseStream()))
{
    source = reader.ReadToEnd();
}
System.IO.StreamWriter file = new System.IO.StreamWriter("c:''test.txt");
file.WriteLine(source);
file.Close();