[Android] PDF 파일 합치기 merge

public static File getMergePDF(ArrayList<File> fileList, String wantFileName, final Activity act) {
        final File outputFile = new File(Cvalue._DOWNLOAD_FOLDER + "/" + wantFileName);
        //    Log.d(CommonUtil.TAG, "outputFile1 > " + outputFile.getAbsolutePath() + " / " + outputFile.length());
        try {
            List<InputStream> pdfs = new ArrayList<InputStream>();
            for (int i = 0; i < fileList.size(); i++) {
                pdfs.add(new FileInputStream(fileList.get(i)));
                Log.d(CommonUtil.TAG, "파일 리스트 : " + fileList.get(i).getAbsolutePath());
            }
            OutputStream output = new FileOutputStream(outputFile);
            //concatPDFs
            Document document = new Document(PageSize.A4);
            try {
                List<PdfReader> readers = new ArrayList<PdfReader>();
                int totalPage = 0;
                //create Reader for PDF Files
                for (InputStream input : pdfs) {
                    PdfReader newReader = new PdfReader(input);
                    readers.add(newReader);
                    totalPage += newReader.getNumberOfPages();
                }
                //create writer for Output
                PdfWriter writer = PdfWriter.getInstance(document, output);
                document.open();

                BaseFont bf = BaseFont.createFont(BaseFont.HELVETICA, BaseFont.CP1252, BaseFont.NOT_EMBEDDED);
                PdfContentByte cb = writer.getDirectContent();      // Holds the PDF

                //data
                PdfImportedPage page;
                int currentPage = 0;
                int pageOfCurrentReaderPDF = 0;

                //add pages
                for (int index = 0; index < readers.size(); index++) {
                    PdfReader reader = readers.get(index);
                    while (pageOfCurrentReaderPDF < reader.getNumberOfPages()) {
                        document.newPage();
                        pageOfCurrentReaderPDF += 1;
                        currentPage += 1;
                        page = writer.getImportedPage(reader, pageOfCurrentReaderPDF);
                        cb.addTemplate(page, 0, 0);

//                      Log.i("TEST", "page > " + currentPage + " of " + totalPage);
                    }

                    File file = fileList.get(index);
                    pageOfCurrentReaderPDF = 0;
                    if (file.exists()) {
//                      Log.i("TEST", "file["+index+"] > " + file.getName() + " delete");
                        //file.delete();
                    } else {
//                      Log.i("TEST", "file["+index+"] > not exist");
                    }
                }
                output.flush();
                document.close();
                output.close();
            } catch (IOException ioe) {
                ioe.printStackTrace();
                //ERROR_MSG = "AUTO_INPUT_OUTPUT_ERROR";
                Log.d(CommonUtil.TAG, "예외처리");
                /*if (act != null && act instanceof Activity) {
                    ((Activity) act).runOnUiThread(new Runnable() {
                        public void run() {
                            Toast.makeText(act, "파일생성중 문제가 발생하였습니다1", Toast.LENGTH_SHORT).show();
                        }
                    });
                }*/
            } catch (DocumentException e) {
                e.printStackTrace();
                Log.d(CommonUtil.TAG, "예외처리2");
                //ERROR_MSG = "DOCUMENT_ERROR";
                /*if (act != null && act instanceof Activity) {
                    ((Activity) act).runOnUiThread(new Runnable() {
                        public void run() {
                            Toast.makeText(act, "파일생성중 문제가 발생하였습니다2", Toast.LENGTH_SHORT).show();
                        }
                    });
                }*/
            } finally {
                if (document.isOpen()) {
                    document.close();
                }
                try {
                    if (output != null) {
                        output.close();
                    }
                } catch (IOException ioe) {
                    ioe.printStackTrace();
                    Log.d(CommonUtil.TAG, "예외처리3");
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
            Log.d(CommonUtil.TAG, "예외처리4");
        }
        Log.d(CommonUtil.TAG, "outputFile2 > " + outputFile.getAbsolutePath() + " / " + outputFile.length());
        return outputFile;
    }

여러장의 PDF 파일을 다운받아 합치기 <MERGE> 하는 방법이다.