load HTML into Microsoft Web Browser control

I am loading a page in the constructor of my form to the Microsoft Web
Browser component:
string URI = "http://some_address.org";
object flags = 0;
object targetframe = "";
object headers = "";
object post = "";
this.axWebBrowser1.Navigate(URI, ref flags,
ref targetframe, ref post, ref headers);

then i am able to create a IHTMLDocument, but i want to parse, modify and
the load it back

private void axWebBrowser1_DocumentComplete(object sender,
AxSHDocVw.DWebBrowserEvents2_DocumentCompleteEvent e)
{
mshtml.IHTMLDocument2 HTMLDocument =
(IHTMLDocument2) axWebBrowser1.Document;
//i want to parse and modify HTMLDocument and load it back to
axWebBrowser1
}

didn't find anything on msdn about this

Any example on how to do it?

I also wrote a function that gets as input the URI and returns a string with
the HTML code of that page, then maybe i could load this string to the
axWebBrowser control, but how?

Would be very grateful for any kind of reply. Sorry for my English.