File myFile = null gives an error tthat says can not declaire a variable of static type 'System.IO.File' please help me ou

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.IO;
using System.Data;
using System.Data.SqlClient;
using System.Text;
using System.Configuration;
using System.Data.Sql;
using System.Media;



namespace PDF_Files
{
    public partial class DownloadFile : System.Web.UI.Page
    {

        File myFile = null;
        protected void Page_Load(object sender, EventArgs e)
        {

            Response.ContentType = "application/x-uknown";
            Response.AppendHeader("Content - Disposiotion", "atachment;filename=\"" + myFile.OriginalName + "\"");
            if (myFile != null)
            {
                Response.BinaryWrite(myFile.FileData);
            }
            else
            {
                Response.WriteFile(Path.Combine(AppConfiguration.UploadFolder, myFile.FileUrl));

            }
        }
    }
}