How to convert the json string into list?

{"SearchDocumentResult":"[{\"ContextType\":\"ddd\",\"ContextIDPrimary\":\"TestContextP\",\"ContextIDSecondary\":\"TestContextS\",\"ContextIDTertiary\":\"\",\"RequirementID\":\"17\",\"Source\":\"image\",\"DocumentName\":\"4.pdf\",\"DocumentImage\":\"\",\"ErrorCode\":\"0\",\"ErrorDescription\":\"\",\"createdBy\":\"\",\"createdDate\":\"12-07-2017 15:39:57\"},{\"ContextType\":\"ddd\",\"ContextIDPrimary\":\"TestContextP\",\"ContextIDSecondary\":\"TestContextS\",\"ContextIDTertiary\":\"\",\"RequirementID\":\"18\",\"Source\":\"image\",\"DocumentName\":\"4.pdf\",\"DocumentImage\":\"\",\"ErrorCode\":\"0\",\"ErrorDescription\":\"\",\"createdBy\":\"\",\"createdDate\":\"12-07-2017 15:42:07\"}]"}

public class test
        {
            public string ContextType { get; set; }
            public string ContextIDPrimary { get; set; }
            public string ContextIDSecondary { get; set; }
            public string ContextIDTertiary { get; set; }
            public string Source{get;set;}
            public string DocumentID { get; set; }
                
        }

public class JsonHelper
   {
       /// <summary>
       /// JSON Serialization
       /// </summary>
       public static string JsonSerializer<T>(T t)
       {
           DataContractJsonSerializer ser = new DataContractJsonSerializer(typeof(T));
           MemoryStream ms = new MemoryStream();
           ser.WriteObject(ms, t);
           string jsonString = Encoding.UTF8.GetString(ms.ToArray());
           ms.Close();
           return jsonString;
       }
       /// <summary>
       /// JSON Deserialization
       /// </summary>
       public static T JsonDeserialize<T>(string jsonString)
       {
           DataContractJsonSerializer ser = new DataContractJsonSerializer(typeof(T));
           MemoryStream ms = new MemoryStream(Encoding.UTF8.GetBytes(jsonString));
           T obj = (T)ser.ReadObject(ms);
           return obj;
       }
   }

public class RootObject
    {
       // public List<SearchDocumentResult> SearchDocumentResult { get; set; }

        public IEnumerable<SearchDocumentResult> SearchDocumentResult { get; set; }

        //public List<Person> People1 { get; set; }
    }

protected void Button1_Click(object sender, EventArgs e)
        {
          

            test t = new test
            {
                ContextType = "ddd",
                ContextIDPrimary = "",
                ContextIDSecondary = "",
                ContextIDTertiary = " ",
                Source = "",
                DocumentID = ""

            };

            DataContractJsonSerializer ser = new DataContractJsonSerializer(typeof(test));
            MemoryStream mem = new MemoryStream();
            ser.WriteObject(mem, t);
            string data = Encoding.UTF8.GetString(mem.ToArray(), 0, (int)mem.Length);
            WebClient webClient = new WebClient();
            webClient.Headers["Content-type"] = "application/json";
            webClient.Encoding = Encoding.UTF8;
            string result = webClient.UploadString("http://192.168.0.151:222/Service1.svc/SearchDocument", "POST", data);

            var result11 = JsonHelper.JsonDeserialize<RootObject1>(result);

            //JavaScriptSerializer serializer = new JavaScriptSerializer();
            //serializer.MaxJsonLength = Int32.MaxValue;
           
           // var a = serializer.Deserialize(result, typeof(object));
          

          // string json = "{\"People\":[{\"FirstName\":\"Hans\",\"LastName\":\"Olo\"},{\"FirstName\":\"Jimmy\",\"LastName\":\"Crackedcorn\"}]}";

          //// var result11 = JsonHelper.JsonDeserialize<RootObject1>(json);

          // var firstNames = result11.People.Select(p => p.FirstName).ToList();
          // var lastNames = result11.People.Select(p => p.LastName).ToList();

        }