using System;

using System.Threading.Tasks;

using AngleSharp;

​

public class Program

{

    public static async Task Main()

    {

        var encodedString = await EncodeString("<p>áêö</p>");

        Console.WriteLine(encodedString);

    }

​

    private static async Task<string> EncodeString(string input)

    {

        var context = BrowsingContext.New(Configuration.Default);

        var document = await context.OpenAsync(req => req.Content(input));

        var pItem = document.QuerySelector("p");

        pItem.TextContent = System.Net.WebUtility.HtmlEncode(pItem.TextContent);

        return pItem.ToHtml();

    }

}