public static string FileName = "test.txt";
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>
FileName.ToFileInfo().WriteAllText(text);
var allText = FileName.ToFileInfo().ReadAllText();
Console.WriteLine(allText);