LoginInformation loginInfo = authApi.Login();

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
using Newtonsoft.Json;

using DocuSign.eSign.Api;
using DocuSign.eSign.Model;
using DocuSign.eSign.Client;

namespace CoreRecipes
{
    class Program
    {
        private string INTEGRATOR_KEY = "[key]";
        static void Main(string[] args)
        {
            Program recipes = new Program();
            recipes.listDocumentsAndDownloadTest();
            Console.Read();
        }
        public void listDocumentsAndDownloadTest()
        {
            string username = "[username]";
            string password = "[password]";
            string envelopeId = "envelopid";
            //configureApiClient("www.docusign.net/restapi");
            //http"s://demo.docusign.net/restapi"
            configureApiClient("https://demo.docusign.net/restpi");
            string accountId = loginApi(username, password);
            EnvelopesApi envelopesApi = new EnvelopesApi();
            EnvelopeDocumentsResult docsList = envelopesApi.ListDocuments(accountId, envelopeId);
            Console.WriteLine("EnvelopeDocumentsResult:n{0}", JsonConvert.SerializeObject(docsList));
            int docCount = docsList.EnvelopeDocuments.Count;
            string filePath = null;
            FileStream fs = null;
            for (int i = 0; i < docCount; i++)
            {
                MemoryStream docStream = (MemoryStream)envelopesApi.GetDocument(accountId, envelopeId, docsList.EnvelopeDocuments[i].DocumentId);
                filePath = Path.GetTempPath() + Path.GetRandomFileName() + ".pdf";
                fs = new FileStream(filePath, FileMode.Create);
                docStream.Seek(0, SeekOrigin.Begin);
                docStream.CopyTo(fs);
                fs.Close();
                Console.WriteLine("Envelope Document {0} has been downloaded to:  {1}", i, filePath);
            }
        }
        public void configureApiClient(string basePath)
        {
            ApiClient apiClient = new ApiClient(basePath);
            Configuration.Default.ApiClient = apiClient;
        }
        public string loginApi(string usr, string pwd)
        {
            ApiClient apiClient = Configuration.Default.ApiClient;
            string authHeader = "{"Username":"" + usr + "", "Password":"" + pwd + "", "IntegratorKey":"" + INTEGRATOR_KEY + ""}";
            Configuration.Default.AddDefaultHeader("X-DocuSign-Authentication", authHeader);
            string accountId = null;
            AuthenticationApi authApi = new AuthenticationApi();
            LoginInformation loginInfo = authApi.Login();
            foreach (LoginAccount loginAcct in loginInfo.LoginAccounts)
            {
                if (loginAcct.IsDefault == "true")
                {
                    accountId = loginAcct.AccountId;
                    break;
                }
            }
            if (accountId == null)
            {
                accountId = loginInfo.LoginAccounts[0].AccountId;
            }
            return accountId;
        }
    }
}

configureApiClient("https://demo.docusign.net/restpi")

configureApiClient("https://demo.docusign.net/restapi")