MVC - 生成多个 PDF

我使用以下代码生成PDF文件。

它运行良好，但现在我想同时生成4 PDF's。

我尝试再次启动Document并重复整个代码以生成第二个PDF报告，但它只生成1个PDF。

            var document = new Document(PageSize.A4, 50, 50, 25, 25);
            // Create a new PdfWrite object, writing the output to a MemoryStream
            var output = new MemoryStream();
            var writer = PdfWriter.GetInstance(document, output);
            // Open the Document for writing
            document.Open();
            string contents = System.IO.File.ReadAllText(Server.MapPath("~/Reports/Original.html"));
            var parsedHtmlElements = HTMLWorker.ParseToList(new StringReader(contents), null);
            foreach (var htmlElement in parsedHtmlElements)
                     document.Add(htmlElement as IElement);    
           document.Close();
           Response.ContentType = "application/pdf";
           Response.AddHeader("Content-Disposition", string.Format("attachment;filename=Receipt-{0}.pdf", "Report"));
           Response.BinaryWrite(output.ToArray());
           return View();

如何生成多个 PDF？