mshtml.HTMLDocument objHtmlDoc = (mshtml.HTMLDocument) webBrowser1.Document.DomDocument;
/*webBrowser1 is the WebBrowser Control showing your page*/
string pageSource = objHtmlDoc.documentElement.innerHTML;
 
/* pageSource string variable will contain the source of the page displayed in your browser control. You can dispaly it in whatever way u wish to */

        private void pageSourceToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Form sourceForm = new Form();
            TextBox sourceCode = new TextBox();
            sourceCode.Dock = DockStyle.Fill;
            sourceCode.Multiline = true;
            sourceCode.ScrollBars = ScrollBars.Both;
            sourceForm.Width = 700;
            sourceForm.Height = 500;
            sourceForm.StartPosition = FormStartPosition.CenterScreen;
            sourceForm.ShowIcon = false;
            sourceForm.ShowInTaskbar = false;
            sourceForm.Text = "Source Code for " + WebBrowser.Url;
            sourceCode.Text = WebBrowser.DocumentText;
            sourceForm.Controls.Add(sourceCode);
            sourceForm.Show(this);
            sourceCode.ReadOnly = true;
        }