public void ConvertRtfToHtml()
{
System.Windows.Forms.WebBrowser webBrowser =
new System.Windows.Forms.WebBrowser();
webBrowser.CreateControl(); // only if needed
webBrowser.DocumentText = richTextBox1.Text;
while (webBrowser.DocumentText != richTextBox1.Text)
Application.DoEvents();
webBrowser.Document.ExecCommand("SelectAll", false, null);
webBrowser.Document.ExecCommand("Copy", false, null);
richTextBox2.Paste();
}