public static MemoryStream Pdf(string html)
        {
            StringReader sr = new StringReader(html);
            //步骤1
            Document document = new Document(PageSize.A4, 10f, 10f, 10f, 0f);

            MemoryStream stream = new MemoryStream();
            //步骤2
            PdfWriter.GetInstance(document, stream);
            //步骤3
            document.Open();

            //创建一个样式表
            StyleSheet styles = new StyleSheet();
            ////设置默认字体的属性
            //styles.LoadTagStyle(HtmlTags.BODY, "encoding", "Identity-H");
            //styles.LoadTagStyle(HtmlTags.BODY, HtmlTags.FONT, "Tahoma");
            //styles.LoadTagStyle(HtmlTags.BODY, "size", "16pt");

            //FontFactory.Register(@"C:\Windows\Fonts\tahoma.ttf");

            var unicodeFontProvider = FontFactoryImp.Instance;
            unicodeFontProvider.DefaultEmbedding = BaseFont.EMBEDDED;
            unicodeFontProvider.DefaultEncoding = BaseFont.IDENTITY_H;

            var props = new Hashtable
            {
            //    { "img_provider", new MyImageFactory() },
                { "font_factory", unicodeFontProvider } //始终使用Unicode字体
            };

            //步骤4
            //var objects = HtmlWorker.ParseToList(sr, styles, props);
            var objects = HtmlWorker.ParseToList(sr, styles);
            foreach (IElement element in objects)
            {
                document.Add(element);
            }

            document.Close();
            return stream;
        }