Can use below tricky method..ints in C# below..
var webBrowser = new WebBrowser();
webBrowser.CreateControl();
webBrowser.DocumentText = *htmltext withtags*;
while (_webBrowser.DocumentText != *yourhtmlstring*)
Application.DoEvents();
webBrowser.Document.ExecCommand("SelectAll", false, null);
webBrowser.Document.ExecCommand("Copy", false, null);
*yourRichTextControl*.Paste();