error in reading html content from asp page

I am creating an HTML template as theme in ASP.NET. I want to read the content of the template on button click and store all the content in another template. I am reading the content as:

 xmlDoc.Load(theme);
            XmlNodeList list开发者_如何学运维 = xmlDoc.SelectNodes("html/body/form/div/table/tbody/tr/td/textarea");
            headtext = list.Item(0).InnerText;
            totext = list.Item(1).InnerText;
            bodytext = list.Item(2).InnerText;
            footertext = list.Item(3).InnerText;
            string new_theme = edittheme(headtext, totext, bodytext, footertext);
            return new_theme ;

but as my asp page contains:

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="theme3.aspx.cs" Inherits="MailCham.theme3" %>

It is giving an error while reading the content. How can i read the content of HTML page?

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Use the HtmlAgilityPack library: here