สอบถามครับเขียน Merge PDF แต่พอเวลาไฟล์เยอะเจอ Error: CombineMultiplePDFs error:Rebuild failed: trailer not found.; Original message: PDF startxref not found.

        public static void CombineMultiplePDFs(string[] fileNames, string outFile)
        {
            try
            {
                PdfReader reader = null;
                PdfImportedPage importedPage;
                // step 1: creation of a document-object
                Document document = new Document();

                // step 2: we create a writer that listens to the document
                PdfCopy writer = new PdfCopy(document, new FileStream(outFile, FileMode.Create));
                if (writer == null)
                {
                    return;
                }


                // step 3: we open the document
                document.Open();

                clsLog.Info("CombineMultiplePDFs outFile : " + outFile);

                foreach (string fileName in fileNames)
                {
                    clsLog.Info("Files :" + fileName);

                    // we create a reader for a certain document
                    if (File.Exists(fileName))
                    {
                        int pages = 0;
                        //PdfReader reader = new PdfReader(fileName);
                        //reader.ConsolidateNamedDestinations();
                        var its = new iTextSharp.text.pdf.PdfReader(fileName);
                        pages = its.NumberOfPages;
                        its.Close();

                        clsLog.Error("CombineMultiplePDFs In Exists : " + fileName);

                        // step 4: we add content
                        //for (int i = 1; i <= reader.NumberOfPages; i++)
                        //{
                        //    clsLog.Error("CombineMultiplePDFs Loop : " + i);
                        //    PdfImportedPage page = writer.GetImportedPage(reader, i);
                        //    writer.AddPage(page);
                        //}

                        reader = new PdfReader(fileName);
                        //Add pages of current file
                        for (int i = 1; i <= pages; i++)
                        {
                            importedPage = writer.GetImportedPage(reader, i);
                            writer.AddPage(importedPage);
                        }
                        //PRAcroForm form = reader.AcroForm;
                        //if (form != null)
                        //{
                        //    clsLog.Error("CombineMultiplePDFs form : null");
                        //    writer.AddDocument(reader);
                        //}

                        reader.Close();

                    }

                }

                // step 5: we close the document and writer
                writer.Close();
                document.Close();

                clsLog.Info("CombineMultiplePDFs End Completed");

            }
            catch (Exception ex)
            {
                clsLog.Error("CombineMultiplePDFs error:" + ex.Message);
                throw new Exception("CombineMultiplePDFs error:" + ex.Message);
            }



        }