//create a folder in server (~/Uploads)
//to upload
File.Copy(@"D:\CORREO.txt", Server.MapPath("~/Uploads/CORREO.txt"));
//to download
Response.ContentType = ContentType;
Response.AppendHeader("Content-Disposition", "attachment;filename=" + Path.GetFileName("~/Uploads/CORREO.txt"));
Response.WriteFile("~/Uploads/CORREO.txt");
Response.End();