public static void mergePDFFiles(List<Stream> fileList, string outMergeFile)
        {
            PdfReader reader;
            Rectangle rec = new Rectangle(1000,1660);
            //Document document = new Document(PageSize.A4.Rotate());
            Document document = new Document();

            PdfWriter writer = PdfWriter.GetInstance(document, new FileStream(outMergeFile, FileMode.Create));
            document.Open();
            PdfContentByte cb = writer.DirectContent;
            PdfImportedPage newPage;

            for (int i = 0; i < fileList.Count; i++)
            {
                reader = new PdfReader(fileList[i]);
                int iPageNum = reader.NumberOfPages;
                for (int j = 1; j <= iPageNum; j++)
                {
                    //获取Reader的pdf页的打印方向
                    var re = reader.GetPageSize(reader.GetPageN(j));
                    //设置合并pdf的打印方向
                    document.SetPageSize(re);
                    //document.SetPageSize(j == 0? PageSize.A4.Rotate() : PageSize.A4);
                    document.NewPage();
                    newPage = writer.GetImportedPage(reader, j);
                    cb.AddTemplate(newPage, 0, 0);
                }
            }
            document.Close();
        }