Highlight text in webbrowser control on mouse doble click C#

private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
        if (webBrowser1.ReadyState == WebBrowserReadyState.Complete)
        {
               HtmlDocument _document = webBrowser1.Document;
               _document.MouseLeave += new HtmlElementEventHandler(document_MouseLeave);

               IHTMLDocument2 currentDoc = (IHTMLDocument2)webBrowser1.Document.DomDocument;
               HTMLDocumentEvents2_Event iEvent = (mshtml.HTMLDocumentEvents2_Event)currentDoc;
               iEvent.ondblclick += new HTMLDocumentEvents2_ondblclickEventHandler(iEvent_ondblclick);
        }
}

private void document_MouseLeave(object sender, HtmlElementEventArgs e)
{
         HtmlElement element = e.FromElement;
         mshtml.HTMLElementEvents2_Event iEvent;
         iEvent = element.DomElement as mshtml.HTMLElementEvents2_Event;
         iEvent.ondblclick -=new HTMLElementEvents2_ondblclickEventHandler(iEvent_ondblclick);
}

bool iEvent_ondblclick(IHTMLEventObj pEvtObj)
{
         if (pEvtObj.srcElement.innerText != null)
         {
               //
               // Stop navigation on current click if it contains link.
               //
               if (pEvtObj.srcElement.outerHTML.Contains("href"))
                      webBrowser1.Stop();

               IHTMLDocument2 doc2 = wbMainPage.Document.DomDocument as IHTMLDocument2;
               StringBuilder html = new StringBuilder(doc2.body.outerHTML);
               String substitution = "" + pEvtObj.srcElement.innerText + "";
               html.Replace(pEvtObj.srcElement.outerHTML, substitution);
               doc2.body.innerHTML = html.ToString();
         }
         return false;
}