Full code sample for DocuSign Request Signature Quickstart - uses open source NuGet Client: https://www.nuget.org/packages/DocuSign.Integration.Client.dll/

RequestSignature.cs

// 
// DocuSign API Quickstart - Embedded Signing 
// 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Diagnostics;

// install DocuSign NuGet package or download source from GitHub:  
// https://www.nuget.org/packages/DocuSign.Integration.Client.dll/
using DocuSign.Integrations.Client;

namespace Quickstart_1
{
    class RequestSignature
    {
        static void Main(string[] args)
        {
            //=======================================================================================================================
            // STEP 1: Login API 
            //=======================================================================================================================

            RestSettings.Instance.DocuSignAddress = "https://demo.docusign.net";
            RestSettings.Instance.WebServiceUrl = RestSettings.Instance.DocuSignAddress + "/restapi/v2";
            RestSettings.Instance.IntegratorKey = "INTEGRATOR_KEY";

            Account account = new Account();
            account.Email = "EMAIL";
            account.Password = "PASSWORD";

            // Login API call (retrieves your baseUrl and accountId)
            bool result = account.Login();

            if (!result)
            {
                Console.WriteLine("Login API call failed for user {0}.\nError Code:  {1}\nMessage:  {2}", account.Email, account.RestError.errorCode, account.RestError.message);
                Console.Read();
                return;
            }

            //=======================================================================================================================
            // STEP 2: Create and Send Envelope API
            //=======================================================================================================================

            // create envelope object and assign login info
            Envelope envelope = new Envelope();
            envelope.Login = account;
            envelope.EmailSubject = "Please sign my document";
            envelope.EmailBlurb = "This goes in the body of the email";
            
            envelope.Recipients = new Recipients()
            {
                signers = new Signer[]
                {
                    new Signer()
                    {
                        email = "RECIPIENT_EMAIL",
                        name = "RECIPIENT NAME",
                        routingOrder = "1",
                        recipientId = "1"
                    }
                }
            };

            Tabs tabList = new Tabs()
            {
                signHereTabs = new Tab[]
                {
                    new Tab()
                    {
                        documentId = 1,
                        pageNumber = 1,
                        xPosition = 100,
                        yPosition = 150
                    }
                }
            };

            // assign our one signHere tab to the recipient
            envelope.Recipients.signers[0].tabs = tabList;

            // "sent" to send immediately, "created" to save as draft
            envelope.Status = "sent";

            //*** Specify document and send the signature request
            result = envelope.Create("C:\\PATH\\TO\\DOCUMENT\\TEST.PDF");

            Console.WriteLine("Signature request has been sent to {0}.", envelope.Recipients.signers[0].email);
            Console.ReadLine(); // pause to show console output
        }
    }
}