// sample usage
CookieManager.SetCookie("key", "value", TimeSpan.FromSeconds(3600));
string value  = CookieManager.GetCookie("value");

// cookie manager class
public class CookieManager
    {

        public static void SetCookie(string key, string val, TimeSpan? expires)
        {

            SetCookie(key, val, expires, null, null, false);
        }

        public static void SetCookie(string key, string val, TimeSpan? expires, string path, string domain, bool secure)
        {

            StringBuilder fullCookie = new StringBuilder();
            fullCookie.Append(string.Concat(key, "=", val));

            if (expires.HasValue)
            {

                DateTime expire = DateTime.UtcNow + expires.Value;
                fullCookie.Append(string.Concat(";expires=", expire.ToString("R")));
            }

            if (path != null)
            {

                fullCookie.Append(string.Concat(";path=", path));
            }

            if (domain != null)
            {

                fullCookie.Append(string.Concat(";domain=", domain));
            }

            if (secure)
            {

                fullCookie.Append(";secure");
            }

            HtmlPage.Document.SetProperty("cookie", fullCookie.ToString());
        }

        public static string GetCookie(String key)
        {
            String[] cookies = HtmlPage.Document.Cookies.Split(';');
            String result = (from c in cookies let keyValues = c.Split('=') where
                                 keyValues.Length == 2 && keyValues[0].Trim() == key.Trim()
                             select keyValues[1]).FirstOrDefault();
            return result;
        }

        public static void DeleteCookie(String key){
            DateTime expir =DateTime.UtcNow -TimeSpan.FromDays(1);
            string cookie =String.Format("{0}=;expires={1}",
            key, expir.ToString("R"));
            HtmlPage.Document.SetProperty("cookie", cookie);
        }

        public static bool Exists(String key, String value)
        {
            return HtmlPage.Document.Cookies.Contains(String.Format("{0}={1}", key, value));
        }
    }

using System;
using System.Windows.Controls;
using System.IO.IsolatedStorage;
using System.IO;

namespace SilverlightApplication10
{
    public class Page : UserControl
    {
        public Page()
        {
            SaveData("Hello There", "MyData.txt");
            if (HasFile("MyData.txt"))
            {
                string test = LoadData("MyData.txt");
            }
        }

        private void SaveData(string data, string fileName)
        {
            IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication();
            IsolatedStorageFileStream isfs = new IsolatedStorageFileStream(fileName, FileMode.Create, isf);
            using (StreamWriter sw = new StreamWriter(isfs))
            {
                sw.Write(data);
                sw.Close();
            }
        }

        private bool HasFile(string fileName)
        {
            IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication();
            return isf.FileExists(fileName);
        }

        private string LoadData(string fileName)
        {
            string data = String.Empty;
            IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication();
            IsolatedStorageFileStream isfs = new IsolatedStorageFileStream(fileName, FileMode.Open, isf);
            using (StreamReader sr = new StreamReader(isfs))
            {
                string lineOfData = String.Empty;
                while ((lineOfData = sr.ReadLine()) != null) data += lineOfData;
            }
            return data;
        }
    }
}