class ConcatN extends AbstractTool {

    static {
        addVersion("$Id: ConcatN.java 3271 2008-04-18 20:39:42Z xlv $");
    }

    /**
     * Constructs a Concat object.
     */
    public ConcatN() {
        menuoptions = MENU_EXECUTE | MENU_EXECUTE_SHOW;
        arguments.add(new FileArrayArgument(this, "srcfiles",
                "The list of PDF files"));
        arguments.add(new FileArgument(this, "destfile",
                "The file to which the concatenated PDF has to be written", true,
                new PdfFilter()));
    }

    /**
     * Concatenates two PDF files.
     *
     * @param args String[]
     */
    public static void main(String[] args) {
        ConcatN tool = new ConcatN();
        if (args.length < 2) {
            System.err.println(tool.getUsage());
        }
        tool.setMainArguments(args);
        tool.execute();
    }

    /**
     * @see com.lowagie.toolbox.AbstractTool#createFrame()
     */
    protected void createFrame() {
        internalFrame = new JInternalFrame("Concatenate n PDF files", true, false, true);
        internalFrame.setSize(300, 80);
        internalFrame.setJMenuBar(getMenubar());
        System.out.println("=== Concat OPENED ===");
    }

    /**
     * @see com.lowagie.toolbox.AbstractTool#execute()
     */
    public void execute() {<FILL_FUNCTION_BODY>}

    /**
     * @param arg StringArgument
     * @see com.lowagie.toolbox.AbstractTool#valueHasChanged(com.lowagie.toolbox.arguments.AbstractArgument)
     */
    public void valueHasChanged(AbstractArgument arg) {
        if (internalFrame == null) {
            // if the internal frame is null, the tool was called from the command line
            return;
        }
        // represent the changes of the argument in the internal frame
    }

    /**
     * @return File
     * @throws InstantiationException on error
     * @see com.lowagie.toolbox.AbstractTool#getDestPathPDF()
     */
    protected File getDestPathPDF() throws InstantiationException {
        return (File) getValue("destfile");
    }

}

        try {
            File[] files;
            if (getValue("srcfiles") == null) {
                throw new InstantiationException(
                        "You need to choose a list of sourcefiles");
            }
            files = ((File[]) getValue("srcfiles"));
            if (getValue("destfile") == null) {
                throw new InstantiationException(
                        "You need to choose a destination file");
            }
            File pdf_file = (File) getValue("destfile");
            int pageOffset = 0;
            List<Map<String, Object>> master = new ArrayList<>();
            Document document = null;
            PdfCopy writer = null;
            for (int i = 0; i < files.length; i++) {
                // we create a reader for a certain document
                PdfReader reader = new PdfReader(files[i].getAbsolutePath());
                reader.consolidateNamedDestinations();
                // we retrieve the total number of pages
                int n = reader.getNumberOfPages();
                List<Map<String, Object>> bookmarks = SimpleBookmark.getBookmarkList(reader);
                if (bookmarks != null) {
                    if (pageOffset != 0) {
                        SimpleBookmark.shiftPageNumbersInRange(bookmarks, pageOffset, null);
                    }
                    master.addAll(bookmarks);
                }
                pageOffset += n;
                System.out.println("There are " + n + " pages in " + files[i]);
                if (i == 0) {
                    // step 1: creation of a document-object
                    document = new Document(reader.getPageSizeWithRotation(1));
                    // step 2: we create a writer that listens to the document
                    writer = new PdfCopy(document,
                            new FileOutputStream(pdf_file));
                    // step 3: we open the document
                    document.open();
                }
                // step 4: we add content
                PdfImportedPage page;
                for (int p = 0; p < n; ) {
                    ++p;
                    page = writer.getImportedPage(reader, p);
                    writer.addPage(page);
                    System.out.println("Processed page " + p);
                }
            }
            if (!master.isEmpty()) {
                writer.setOutlines(master);
            }
            // step 5: we close the document
            document.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    
<methods>public void <init>() ,public void actionPerformed(java.awt.event.ActionEvent) ,public abstract void execute() ,public ArrayList<com.lowagie.toolbox.arguments.AbstractArgument> getArguments() ,public javax.swing.JInternalFrame getInternalFrame() ,public javax.swing.JMenuBar getMenubar() ,public java.lang.String getUsage() ,public java.lang.Object getValue(java.lang.String) throws java.lang.InstantiationException,public void setArguments(ArrayList<com.lowagie.toolbox.arguments.AbstractArgument>) ,public void setInternalFrame(javax.swing.JInternalFrame) ,public void setMainArguments(java.lang.String[]) ,public void setMenubar(javax.swing.JMenuBar) ,public abstract void valueHasChanged(com.lowagie.toolbox.arguments.AbstractArgument) <variables>public static final int MENU_EXECUTE,public static final int MENU_EXECUTE_PRINT,public static final int MENU_EXECUTE_PRINT_SILENT,public static final int MENU_EXECUTE_SHOW,protected ArrayList<com.lowagie.toolbox.arguments.AbstractArgument> arguments,private java.awt.Desktop awtdesktop,protected javax.swing.JInternalFrame internalFrame,private javax.swing.JMenuBar menubar,protected int menuoptions,public static ArrayList<java.lang.String> versionsarray