public static void Main()
<h1>This is <b>bold</b> heading</h1>
<p>This is <u>underlined</u> paragraph</p>
<h2>This is <i>italic</i> heading</h2>
<h2>This is new heading</h2>
var htmlDoc = new HtmlDocument();
TextWriter writer = File.CreateText("TextWriter.html");
var node = htmlDoc.DocumentNode.SelectSingleNode("//body");
node.WriteContentTo(writer);
var htmlNewDoc = new HtmlDocument();
htmlNewDoc.Load("TextWriter.html");
var result = htmlNewDoc.DocumentNode.OuterHtml;
Console.WriteLine(result);