using( RichEditControl selector = new RichEditControl() {

RtfText = richTextFromHtml

} ) {

DocumentRange rangeBlockOne = selector.Document.CreateRange( ,  );

DocumentRange rangeBlockTwo = selector.Document.CreateRange( ,  );

richTextBlockOne = selector.Document.GetRtfText( rangeBlockOne );

richTextBlockTwo = selector.Document.GetRtfText( rangeBlockTwo );

}