C#

using System;
using System.Threading.Tasks;
using MyApp.FileTransfer;
using MyApp.Client.Classes;

namespace MyApp.Client.FileTransfer
{
    public class LANFileTransfer : IFileTransfer
    {
        #region Public Methods
        // Copy a file to/from the server
        public async void DownloadFile(string sourceFile, string destFile)
        {
            await Task.Run(async () => 
            {
                await TransferFile(sourceFile, destFile);
            }).ContinueWith((t) => FileTransferComplete(t));
        }
        #endregion

        #region Private Methods

        // Called when the file transfer has completed
        private void FileTransferComplete(Task task)
        {
        }

        // Report progress on the file
        private void FileTransferProgress(double percentage)
        {
        }

        // Copy the file
        private async Task TransferFile(string sourceFile, string destFile)
        {
            IProgress<double> progress = new Progress<double>(FileTransferProgress);
            await FileEx.CopyAsync(sourceFile, destFile, progress);
        }

        #endregion
    }
}

using (MemoryStream memoryStream = new MemoryStream())
{

    document.Save(memoryStream, false);

    memoryStream.Position = 0;


    Session["BinaryData"] = memoryStream.ToArray();

    ScriptManager.RegisterStartupScript(this, this.GetType(), "openPDF", "javascript:window.open('../../Service/Pages/Page2.aspx');", true);

    Response.Redirect('../../Service/Pages/Page3.aspx');
}

protected void Page_Load(object sender, EventArgs e)
       {
           if (Session["BinaryData"] != null)
           {

               Response.Clear();
               Response.ContentType = "application/pdf";
               Response.AddHeader("Content-Disposition", "inline; filename=" + filename);
               ////Write the MemoryStream to the Response.
               Response.BinaryWrite((byte[])Session["BinaryData"]);
           }