this will work perfectly 
we need to add webbrowser with threading other wise we will get ActiveX control '8856f961-340a-11d0-a96b-00c04fd705a2' cannot be instantiated because the current thread is not in a single-threaded apartment. error
this is the way we can make webbrowser work in asp.net webpages
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Threading;
using System.Windows.Forms;
/// <summary>
/// Summary description for CustomBrowser
/// </summary>
public class CustomBrowser
{
    public CustomBrowser()
    {
        //
        // TODO: Add constructor logic here
        //
    }
    protected string _url;
    string html = "";
    public string GetWebpage(string url)
    {
        _url = url;
        // WebBrowser is an ActiveX control that must be run in a
        // single-threaded apartment so create a thread to create the
        // control and generate the thumbnail
        Thread thread = new Thread(new ThreadStart(GetWebPageWorker));
        thread.SetApartmentState(ApartmentState.STA);
        thread.Start();
        thread.Join();
        string s = html;
        return s;
    }
    protected void GetWebPageWorker()
    {
        using (WebBrowser browser = new WebBrowser())
        {
            //  browser.ClientSize = new Size(_width, _height);
            browser.ScrollBarsEnabled = false;
            browser.ScriptErrorsSuppressed = true;
            browser.Navigate(_url);
            // Wait for control to load page
            while (browser.ReadyState != WebBrowserReadyState.Complete)
                Application.DoEvents();
            html = browser.DocumentText;
        }
    }
}
in webpage
CustomBrowser browser = new CustomBrowser();
string s = browser.GetWebpage("http://localhost:8781/WebSite3/Default3.aspx");
Response.Write(s);