Program.cs

using Microsoft.Azure.Documents;
using Microsoft.Azure.Documents.Client;
using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DocDbToString
{
    class Program
    {
        const string DBLINK = "[DBLINK]";
        const string COLLECTIONLINK = "[COLLECTIONLINK]";
        const string ENDPOINT = "https://your.endpoint";
        const string AUTHKEY = "[AUTHKEY]";
        static void Main(string[] args)
        {
            Run().Wait();
        }

        static async System.Threading.Tasks.Task Run()
        {
            
            using (var client = new DocumentClient(new Uri(ENDPOINT), AUTHKEY))
            {
                var task = new Task
                {
                    Name = "Hello",
                    Reminders = new List<Reminder> { new Reminder { Reminded = false } }
                };

                var database = new Database();
                database = await client.ReadDatabaseAsync(DBLINK);

                var collection = new DocumentCollection();
                collection = await client.ReadDocumentCollectionAsync(COLLECTIONLINK);
                
                var taskDoc = await client.CreateDocumentAsync(collection.SelfLink, task);

                //Read document 
                var newTask = (Task)(dynamic)(await client.ReadDocumentAsync(taskDoc.Resource.SelfLink)).Resource;

                newTask.Reminders.First().Reminded = true;
                Console.WriteLine(newTask.Reminders.First().Reminded);
                Console.WriteLine(newTask.ToString());
                await client.ReplaceDocumentAsync(newTask);
            }
        }
    }

    public class Task : Document
    {
        [JsonProperty(PropertyName = "name")]
        public string Name { get; set; }

        [JsonProperty(PropertyName = "reminders")]
        public IEnumerable<Reminder> Reminders { get; set; }
    }

    public class Reminder
    {
        [JsonProperty(PropertyName = "reminded")]
        public bool Reminded { get; set; }
    }
}