To get a string that represents HTML of loaded web page use the Browser.GetHTML() method. You must call this method only when web page is loaded completely. Otherwise you might receive incomplete HTML or empty string. The following code demonstrates how to wait until web page is loaded completely and get HTML of loaded web page: 

C#

using System;
using DotNetBrowser;
using DotNetBrowser.Events;

namespace MyNamespace
{
    class Program
    {
        static void Main(string[] args)
        {
            // Create Browser instance.
            Browser browser = BrowserFactory.Create();

            // Register frame loading event listener.
            browser.FinishLoadingFrameEvent += delegate(object sender, FinishLoadingEventArgs e)
            {
                // Wait until main document of the web page is loaded completely.
                if (e.IsMainFrame)
                {
                    // Get HTML of the loaded web page and write it to Console.
                    Console.Out.WriteLine(e.Browser.GetHTML());
                }
            };

            // Load teamdev.com to get its HTML content.
            browser.LoadURL("http://www.teamdev.com");
        }
    }
}

VB.NET

Imports DotNetBrowser

Module MyNamespace
    Sub Main()

        'Create Browser instance.
        Dim browser As Browser = BrowserFactory.Create()

        'Register frame loading event listener.
        AddHandler browser.FinishLoadingFrameEvent, Sub(sender, e)

            'Wait until main document of the web page is loaded completely.
            If (e.IsMainFrame) Then

                'Get HTML of the loaded web page and write it to Console.
                Console.Out.WriteLine(e.Browser.GetHTML())
            End If
        End Sub

        'Load teamdev.com to get its HTML content.
        browser.LoadURL("http://www.teamdev.com")
    End Sub
End Module