Download Async won't finish the download c#

Question

i'm trying to make an updater that will download from an url with webclient in async mode.

But it cut my download and don't download the full file.

Here's the code :

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Net;
using System.Diagnostics;

namespace Updater
{
  public partial class Form1 : Form
  {
    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        WebClient Client = new WebClient();

        Client.DownloadFileCompleted += new AsyncCompletedEventHandler(Completed);
        Client.DownloadFileAsync(new Uri("http://localhost/launcher/"), @"C:\launcher.exe");
    }

    private void Completed(object sender, AsyncCompletedEventArgs e)
    {

        if (e.Error != null)
        {
            string error = e.Error.ToString();
            // or
            // error = "Your error message here";

            MessageBox.Show(error);
            return;
        }

        if (e.Cancelled == true)
        {
        }
        else
        {
            Close();
        }

    }
}

}

I'm new with c# and still can't figure where's my error. :/ ty

edit :

I missed to say to download the file launcher.exe at this :

 Client.DownloadFileAsync(new Uri("http://localhost/launcher/"), @"C:\launcher.exe");

to this

 Client.DownloadFileAsync(new Uri("http://localhost/launcher/launcher.exe"), @"C:\launcher.exe");

thanks to Адизбек Эргашев for his links and where it help me : https://stackoverflow.com/a/26232827/6495475