C# Online Compiler | .NET Fiddle

<no name> by Anonymous

using System;
using HtmlAgilityPack;
using System.IO;
					
public class Program
{
	public static void Main()
	{
		var html = @"<html><head><meta name=""Generator"" content=""Microsoft Exchange Server"">
<!-- converted from text -->
<style><!-- .EmailQuote { margin-left: 1pt; padding-left: 4pt; border-left: #800000 2px solid; } --></style></head>
<body>
<font size=""2""><span style=""font-size:11pt;""><div class=""PlainText""> <p>Hello world, how are you doing today?</p><p>This is a separate <b>paragraph</b></p></div></span></font>
</body>
</html>";
		var plainText = ConvertHtml(html);
		Console.WriteLine(plainText);
	}
	public static string Convert(string path)
    {
        HtmlDocument doc = new HtmlDocument();
        doc.Load(path);

        StringWriter sw = new StringWriter();
        ConvertTo(doc.DocumentNode, sw);
        sw.Flush();
        return sw.ToString();
    }

    public static string ConvertHtml(string html)
    {
        HtmlDocument doc = new HtmlDocument();
        doc.LoadHtml(html);

        StringWriter sw = new StringWriter();
        ConvertTo(doc.DocumentNode, sw);
        sw.Flush();
        return sw.ToString();
    }

    public static void ConvertContentTo(HtmlNode node, TextWriter outText)
    {
        foreach(HtmlNode subnode in node.ChildNodes)
        {
            ConvertTo(subnode, outText);
        }
    }

    public static void ConvertTo(HtmlNode node, TextWriter outText)
    {
        string html;
        switch(node.NodeType)
        {
            case HtmlNodeType.Comment:
                // don't output comments
                break;

            case HtmlNodeType.Document:
                ConvertContentTo(node, outText);
                break;

            case HtmlNodeType.Text:
                // script and style must not be output
                string parentName = node.ParentNode.Name;
                if ((parentName == "script") || (parentName == "style"))
                    break;

                // get text
                html = ((HtmlTextNode)node).Text;

                // is it in fact a special closing node output as text?
                if (HtmlNode.IsOverlappedClosingElement(html))
                    break;

                // check the text is meaningful and not a bunch of whitespaces
                if (html.Trim().Length > 0)
                {
                    outText.Write(HtmlEntity.DeEntitize(html));
                }
                break;

            case HtmlNodeType.Element:
                switch(node.Name)
                {
                    case "p":
                        // treat paragraphs as crlf
                        outText.Write("\r\n");
                        break;
                }

                if (node.HasChildNodes)
                {
                    ConvertContentTo(node, outText);
                }
                break;
        }
	}
}

​x
 
using System;
using HtmlAgilityPack;
using System.IO;
                    
public class Program
{
    public static void Main()
    {
        var html = @"<html><head><meta name=""Generator"" content=""Microsoft Exchange Server"">
<!-- converted from text -->
<style><!-- .EmailQuote { margin-left: 1pt; padding-left: 4pt; border-left: #800000 2px solid; } --></style></head>
<body>
<font size=""2""><span style=""font-size:11pt;""><div class=""PlainText""> <p>Hello world, how are you doing today?</p><p>This is a separate <b>paragraph</b></p></div></span></font>
</body>
</html>";
        var plainText = ConvertHtml(html);
        Console.WriteLine(plainText);
    }
    public static string Convert(string path)
    {
        HtmlDocument doc = new HtmlDocument();
        doc.Load(path);
​
        StringWriter sw = new StringWriter();
        ConvertTo(doc.DocumentNode, sw);
        sw.Flush();
        return sw.ToString();
    }
​
    public static string ConvertHtml(string html)
    {
        HtmlDocument doc = new HtmlDocument();
        doc.LoadHtml(html);
​
        StringWriter sw = new StringWriter();
        ConvertTo(doc.DocumentNode, sw);
        sw.Flush();
        return sw.ToString();
    }
​
    public static void ConvertContentTo(HtmlNode node, TextWriter outText)
    {
        foreach(HtmlNode subnode in node.ChildNodes)
        {
            ConvertTo(subnode, outText);
        }
    }
​
    public static void ConvertTo(HtmlNode node, TextWriter outText)
    {
        string html;
        switch(node.NodeType)
        {
            case HtmlNodeType.Comment:
                // don't output comments
                break;
​
            case HtmlNodeType.Document:
                ConvertContentTo(node, outText);
                break;
​
            case HtmlNodeType.Text:
                // script and style must not be output
                string parentName = node.ParentNode.Name;
                if ((parentName == "script") || (parentName == "style"))
                    break;
​
                // get text
                html = ((HtmlTextNode)node).Text;
​
                // is it in fact a special closing node output as text?
                if (HtmlNode.IsOverlappedClosingElement(html))
                    break;
​
                // check the text is meaningful and not a bunch of whitespaces
                if (html.Trim().Length > 0)
                {
                    outText.Write(HtmlEntity.DeEntitize(html));
                }
                break;
​
            case HtmlNodeType.Element:
                switch(node.Name)
                {
                    case "p":
                        // treat paragraphs as crlf
                        outText.Write("\r\n");
                        break;
                }
​
                if (node.HasChildNodes)
                {
                    ConvertContentTo(node, outText);
                }
                break;
        }
    }
}

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