Downloading files without direct address through C# program

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Text.RegularExpressions;
using System.Net;
using System.IO;

namespace UNDocs
{
    public partial class Form1 : Form
    {
        private const string StartingPage = @"http://www.un.org/depts/dhl/resguide/r1.htm";
        private const string CookieOriginator = @"http://daccess-dds-ny.un.org/prod/ods_mother.nsf?Login&Username=freeods2&Password=1234";

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            //Load all of the links in the Listbox
            string html = GetHTML(StartingPage);

            MatchCollection matches = GetLinks(html);

            foreach (Match match in matches)
            {
                string value = match.Groups["link"].Value;

                listBox1.Items.Add(value);
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            //Get the temporary page to redirect to
            string tempPage = GetURLBase(listBox1.SelectedItem.ToString()) +
                              GetPageToRedirectTo(listBox1.SelectedItem.ToString(), StartingPage);

            //Get the cookies to use
            CookieContainer cookies = GetCookies(CookieOriginator, tempPage);

            //This is the page with the link to the actual page
            string finalPage = GetPageToRedirectTo(tempPage);

            //Get the byte array representing the pdf file
            byte[] pdf = GetBytesFromHTTP(finalPage, cookies);

            //write the file to disk
            WriteFile(@"D:\temp.pdf", pdf);
        }

        public MatchCollection GetLinks(string s)
        {
            Regex regex = new Regex("href=\"(?<link>.*?)\"", RegexOptions.Multiline);
            return regex.Matches(s);
        }

        public string GetHTML(string url)
        {
            return GetHTML(url, "");
        }

        public string GetHTML(string url, string Referer)
        {
            return GetHTML(url, Referer, new CookieContainer());
        }
     
        public string GetHTML(string url, string Referer, CookieContainer cookies)
        {
            HttpWebRequest myRequest = (HttpWebRequest)HttpWebRequest.Create(url);
            myRequest.Referer = Referer;
            myRequest.CookieContainer = cookies;

            string pageSource = "";

            using (HttpWebResponse response = (HttpWebResponse)myRequest.GetResponse())
            {
                using (StreamReader reader = new StreamReader(response.GetResponseStream()))
                {
                    pageSource = reader.ReadToEnd();
                }
            }

            return pageSource;
        }

        public byte[] GetBytesFromHTTP(string url, CookieContainer cookies)
        {
            HttpWebRequest myRequest = (HttpWebRequest)HttpWebRequest.Create(url);
            myRequest.CookieContainer = cookies;
            myRequest.Headers.Add(HttpRequestHeader.AcceptEncoding, "gzip,deflate");

            byte[] result = null;
            byte[] buffer = new byte[4096];

            using (HttpWebResponse response = (HttpWebResponse)myRequest.GetResponse())
            {
                using (Stream responseStream = response.GetResponseStream())
                {
                    using (MemoryStream memoryStream = new MemoryStream())
                    {
                        int count = 0;

                        do
                        {
                            count = responseStream.Read(buffer, 0, buffer.Length);
                            memoryStream.Write(buffer, 0, count);
                        } while (count != 0);

                        result = memoryStream.ToArray();
                    }
                }
            }

            return result;
        }

        private string GetURLBase(string url)
        {
            Regex regex = new Regex("(?<base>http://.*?)/");
            return regex.Match(url).Groups["base"].Value;
        }

        private string GetPageToRedirectTo(string url)
        {
            return GetPageToRedirectTo(url, "");
        }

        private string GetPageToRedirectTo(string url, string Referer)
        {
            HttpWebRequest myRequest = (HttpWebRequest)HttpWebRequest.Create(url);
            myRequest.Referer = Referer;

            string pageSource = "";

            using (HttpWebResponse response = (HttpWebResponse)myRequest.GetResponse())
            {
                using (StreamReader reader = new StreamReader(response.GetResponseStream()))
                {
                    pageSource = reader.ReadToEnd();
                }
            }

            string urlToRedirectTo = "";

            //Get URL in Meta Tag
            Regex regex = new Regex("<META.*URL=(?<URL>.*)\"");
            urlToRedirectTo = regex.Match(pageSource).Groups["URL"].Value;

            return urlToRedirectTo;
        }

        private CookieContainer GetCookies(string url, string Referer)
        {
            HttpWebRequest myRequest = (HttpWebRequest)HttpWebRequest.Create(url);
            myRequest.Referer = Referer;
            myRequest.CookieContainer = new CookieContainer();
            myRequest.GetResponse().Close();

            return myRequest.CookieContainer;
        }

        public void WriteFile(string FileName, byte[] fileContents)
        {
            FileStream outFile = new FileStream(FileName, FileMode.Create);

            using (BinaryWriter writer = new BinaryWriter(outFile))
            {
                writer.Write(fileContents, 0, fileContents.Length);
            }

            outFile.Dispose();
        }
    }
}