HtmlNodeCollection children = _doc.DocumentNode.SelectSingleNode("//body").ChildNodes;
Foreach(HtmlNode node in children)
{
     string text = node.InnerText.ToLower();
     string linkText = string.Join(" ", node.SelectNodes("//a").Select(x=>x.InnerText).ToList());
}

HtmlDocument doc = new HtmlDocument()
doc.LoadHtml(node.OuterHtml)
string linkText = string.Join(" ", doc.DocumentNode.SelectNodes("//a").Select(x=>x.InnerText).ToList());