Converting HTML to Plain Text in C#:

Below is a simple C# program that shows this conversion:

using System;
using System.Text.RegularExpressions;

class Program
{
    static void Main(string[] args)
    {
        string htmlContent = "<h1>Hello, <em>world</em>!</h1>";
        string plainText = StripHtmlTags(htmlContent);
        Console.WriteLine(plainText);
    }

    static string StripHtmlTags(string html)
    {
        return Regex.Replace(html, "<.*?>", string.Empty);
    }
}

We defined a method called StripHtmlTags, which takes an HTML string as input and uses a regular expression to remove all HTML tags from it. The Main method shows how to use this function by providing sample HTML content and printing the resulting plain text.

Output:

Hello, world!