Я нашел решение. Работает фантастически!
mshtml.IHTMLDocument2 doc = (IHTMLDocument2)MainBrowser.Document;
if (null != doc)
{
foreach (IHTMLElement element in doc.all)
{
if (element.id == "wrapper")
{
HTMLDivElement container = element as HTMLDivElement;
dynamic dd = container;
string result = dd.IHTMLElement_innerHTML;
// You get ANY member of HTMLDivElementClass
break;
}
}
}