This is Customized PDFDebugger That shows understandable Tree string for tree nodes when clicked

CustomizedPDFDebugger.java

package org.apache.pdfbox;

import org.apache.pdfbox.cos.*;
import org.apache.pdfbox.pdfviewer.ArrayEntry;
import org.apache.pdfbox.pdfviewer.MapEntry;
import org.apache.pdfbox.pdfviewer.PDFTreeCellRenderer;
import org.apache.pdfbox.pdfviewer.PDFTreeModel;
import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.util.ExtensionFileFilter;

import javax.swing.*;
import javax.swing.tree.TreeModel;
import javax.swing.tree.TreePath;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

/**
 * Created by kbashar on 3/10/15.
 */
public class PDFDebuggerCustomized extends JFrame {
    private File currentDir=new File(".");
    private PDDocument document = null;

    private static final String NONSEQ = "-nonSeq";
    private static final String PASSWORD = "-password";

    private static boolean useNonSeqParser = false;

    /**
     * Constructor.
     */
    public PDFDebuggerCustomized()
    {
        initComponents();
    }

    /**
     * This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
     */
    private void initComponents()
    {
        jSplitPane1 = new javax.swing.JSplitPane();
        jScrollPane1 = new javax.swing.JScrollPane();
        jTree1 = new javax.swing.JTree();
        jScrollPane2 = new javax.swing.JScrollPane();
        jTextPane1 = new javax.swing.JTextPane();
        menuBar = new javax.swing.JMenuBar();
        fileMenu = new javax.swing.JMenu();
        openMenuItem = new javax.swing.JMenuItem();
        saveMenuItem = new javax.swing.JMenuItem();
        saveAsMenuItem = new javax.swing.JMenuItem();
        exitMenuItem = new javax.swing.JMenuItem();
        editMenu = new javax.swing.JMenu();
        cutMenuItem = new javax.swing.JMenuItem();
        copyMenuItem = new javax.swing.JMenuItem();
        pasteMenuItem = new javax.swing.JMenuItem();
        deleteMenuItem = new javax.swing.JMenuItem();
        helpMenu = new javax.swing.JMenu();
        contentsMenuItem = new javax.swing.JMenuItem();
        aboutMenuItem = new javax.swing.JMenuItem();

        jTree1.setCellRenderer( new PDFTreeCellRenderer() );
        jTree1.setModel( null );

        setTitle("PDFBox - PDF Viewer");
        addWindowListener(new java.awt.event.WindowAdapter()
        {
            public void windowClosing(java.awt.event.WindowEvent evt)
            {
                exitForm(evt);
            }
        });


        jScrollPane1.setBorder(new javax.swing.border.BevelBorder(javax.swing.border.BevelBorder.RAISED));
        jScrollPane1.setPreferredSize(new java.awt.Dimension(300, 500));
        jTree1.addTreeSelectionListener(new javax.swing.event.TreeSelectionListener()
        {
            public void valueChanged(javax.swing.event.TreeSelectionEvent evt)
            {
                jTree1ValueChanged(evt);
            }
        });

        jScrollPane1.setViewportView(jTree1);

        jSplitPane1.setRightComponent(jScrollPane2);

        jScrollPane2.setPreferredSize(new java.awt.Dimension(300, 500));
        jScrollPane2.setViewportView(jTextPane1);

        jSplitPane1.setLeftComponent(jScrollPane1);

        JScrollPane documentScroller = new JScrollPane();
        //documentScroller.setPreferredSize( new Dimension( 300, 500 ) );
        documentScroller.setViewportView( documentPanel );

        getContentPane().add( jSplitPane1, java.awt.BorderLayout.CENTER );

        fileMenu.setText("File");
        openMenuItem.setText("Open");
        openMenuItem.setToolTipText("Open PDF file");
        openMenuItem.addActionListener(new java.awt.event.ActionListener()
        {
            public void actionPerformed(java.awt.event.ActionEvent evt)
            {
                openMenuItemActionPerformed(evt);
            }
        });

        fileMenu.add(openMenuItem);

        saveMenuItem.setText("Save");

        saveAsMenuItem.setText("Save As ...");

        exitMenuItem.setText("Exit");
        exitMenuItem.addActionListener(new java.awt.event.ActionListener()
        {
            public void actionPerformed(java.awt.event.ActionEvent evt)
            {
                exitMenuItemActionPerformed(evt);
            }
        });

        fileMenu.add(exitMenuItem);

        menuBar.add(fileMenu);

        editMenu.setText("Edit");
        cutMenuItem.setText("Cut");
        editMenu.add(cutMenuItem);

        copyMenuItem.setText("Copy");
        editMenu.add(copyMenuItem);

        pasteMenuItem.setText("Paste");
        editMenu.add(pasteMenuItem);

        deleteMenuItem.setText("Delete");
        editMenu.add(deleteMenuItem);

        helpMenu.setText("Help");
        contentsMenuItem.setText("Contents");
        helpMenu.add(contentsMenuItem);

        aboutMenuItem.setText("About");
        helpMenu.add(aboutMenuItem);

        setJMenuBar(menuBar);


        java.awt.Dimension screenSize = java.awt.Toolkit.getDefaultToolkit().getScreenSize();
        setBounds((screenSize.width-700)/2, (screenSize.height-600)/2, 700, 600);
    }//GEN-END:initComponents

    private void openMenuItemActionPerformed(java.awt.event.ActionEvent evt)
    {
        JFileChooser chooser = new JFileChooser();
        chooser.setCurrentDirectory(currentDir);

        ExtensionFileFilter pdfFilter = new ExtensionFileFilter(new String[] {"pdf", "PDF"}, "PDF Files");
        chooser.setFileFilter(pdfFilter);
        int result = chooser.showOpenDialog(PDFDebuggerCustomized.this);
        if (result == JFileChooser.APPROVE_OPTION)
        {
            String name = chooser.getSelectedFile().getPath();
            currentDir = new File(name).getParentFile();
            try
            {
                readPDFFile(name, "");
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }
        }
    }//GEN-LAST:event_openMenuItemActionPerformed

    private void jTree1ValueChanged(javax.swing.event.TreeSelectionEvent evt)
    {
        TreePath path = jTree1.getSelectionPath();
        if (path != null)
        {
            try
            {
                Object selectedNode = path.getLastPathComponent();
                String data=convertToString(selectedNode);



                if (data != null)
                {
                    jTextPane1.setText(data);
                }
                else
                {
                    jTextPane1.setText( "" );
                }
                printPath(path);
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }
        }
    }//GEN-LAST:event_jTree1ValueChanged

    private String convertToString( Object selectedNode )
    {
        String data = null;
        if(selectedNode instanceof COSBoolean)
        {
            data = "" + ((COSBoolean)selectedNode).getValue();
        }
        else if( selectedNode instanceof COSFloat)
        {
            data = "" + ((COSFloat)selectedNode).floatValue();
        }
        else if( selectedNode instanceof COSNull)
        {
            data = "null";
        }
        else if( selectedNode instanceof COSInteger)
        {
            data = "" + ((COSInteger)selectedNode).intValue();
        }
        else if( selectedNode instanceof COSName)
        {
            data = "" + ((COSName)selectedNode).getName();
        }
        else if( selectedNode instanceof COSString )
        {
            data = "" + ((COSString)selectedNode).getString();
        }
        else if( selectedNode instanceof COSStream )
        {
            try
            {
                COSStream stream = (COSStream)selectedNode;
                InputStream ioStream = stream.getUnfilteredStream();
                ByteArrayOutputStream byteArray = new ByteArrayOutputStream();
                byte[] buffer = new byte[1024];
                int amountRead = 0;
                while( (amountRead = ioStream.read( buffer, 0, buffer.length ) ) != -1 )
                {
                    byteArray.write( buffer, 0, amountRead );
                }
                data = byteArray.toString();
            }
            catch( IOException e )
            {
                e.printStackTrace();
            }
        }
        else if( selectedNode instanceof MapEntry)
        {
            data = convertToString( ((MapEntry)selectedNode).getValue() );
        }
        else if( selectedNode instanceof ArrayEntry)
        {
            data = convertToString( ((ArrayEntry)selectedNode).getValue() );
        }
        return data;
    }

    private void printPath(TreePath path)
    {
        StringBuilder pathStringBuilder = new StringBuilder();
        while (path.getParentPath()!=null)
        {
            Object object = path.getLastPathComponent();
            pathStringBuilder.insert(0,"/"+getObjectName(object));
            path = path.getParentPath();
        }
        pathStringBuilder.deleteCharAt(0);
        System.out.println(pathStringBuilder.toString());
    }

    private String getObjectName(Object object)
    {
        String name = "";
        if( object instanceof MapEntry )
        {
            MapEntry entry = (MapEntry)object;
            COSName key = (COSName)entry.getKey();

            name = key.getName();
        }
        else if( object instanceof ArrayEntry )
        {
            ArrayEntry entry = (ArrayEntry)object;
            name =  "[" + entry.getIndex() + "]";
        }
        else if( object instanceof COSDictionary )
        {
            COSDictionary dict = (COSDictionary)object;
            if( object instanceof COSStream )
            {
                name = "Stream";
            }
            else
            {
                name = "Dictionary";
            }

            COSName type = (COSName)dict.getDictionaryObject( COSName.TYPE );
            if( type != null )
            {
                name = name + "(" + type.getName();
                COSName subType = (COSName)dict.getDictionaryObject( COSName.SUBTYPE );
                if( subType != null )
                {
                    name = name + ":" + subType.getName();
                }

                name = name + ")";
            }
        }
        else if( object instanceof COSArray )
        {
            name="Array";
        }
        else
        {
            throw new RuntimeException( "Unknown COS type " + object.getClass().getName() );
        }
        return name;
    }

    private void exitMenuItemActionPerformed(java.awt.event.ActionEvent evt)
    {
        if( document != null )
        {
            try
            {
                document.close();
            }
            catch( IOException io )
            {
                io.printStackTrace();
            }
        }
        System.exit(0);
    }

    /**
     * Exit the Application.
     */
    private void exitForm(java.awt.event.WindowEvent evt)
    {
        if( document != null )
        {
            try
            {
                document.close();
            }
            catch( IOException io )
            {
                io.printStackTrace();
            }
        }
        System.exit(0);
    }

    /**
     * @param args the command line arguments
     *
     * @throws Exception If anything goes wrong.
     */
    public static void main(String[] args) throws Exception
    {
        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        PDFDebuggerCustomized viewer = new PDFDebuggerCustomized();
        String filename = null;
        String password = "";
        for( int i = 0; i < args.length; i++ )
        {
            if( args[i].equals( PASSWORD ) )
            {
                i++;
                if( i >= args.length )
                {
                    usage();
                }
                password = args[i];
            }
            if( args[i].equals( NONSEQ ) )
            {
                useNonSeqParser = true;
            }
            else
            {
                filename = args[i];
            }
        }

        if (filename != null)
        {
            viewer.readPDFFile( filename, password );
        }
        viewer.setVisible(true);
    }

    private void readPDFFile(String file, String password) throws Exception
    {
        if( document != null )
        {
            document.close();
        }
        File f = new File( file );
        parseDocument( f, password );
        TreeModel model=new PDFTreeModel(document);
        jTree1.setModel(model);
        setTitle( "PDFBox - " + f.getAbsolutePath() );
    }
    /**
     * This will parse a document.
     *
     * @param file The file addressing the document.
     *
     * @throws IOException If there is an error parsing the document.
     */
    private void parseDocument( File file, String password )throws IOException
    {
        if (useNonSeqParser)
        {
            document = PDDocument.loadNonSeq(file, null, password);
        }
        else
        {
            document = PDDocument.load( file );
            if( document.isEncrypted() )
            {
                try
                {
                    document.decrypt( password );
                }
                catch( org.apache.pdfbox.exceptions.CryptographyException e )
                {
                    e.printStackTrace();
                }
            }
        }
    }

    /**
     * This will print out a message telling how to use this utility.
     */
    private static void usage()
    {
        System.err.println(
                "usage: java -jar pdfbox-app-x.y.z.jar PDFDebugger [OPTIONS] <input-file>\n" +
                        "  -password <password>      Password to decrypt the document\n" +
                        "  -nonSeq                   Enables the new non-sequential parser\n" +
                        "  <input-file>              The PDF document to be loaded\n"
        );
    }

    // Variables declaration - do not modify//GEN-BEGIN:variables
    private javax.swing.JMenuItem aboutMenuItem;
    private javax.swing.JMenuItem contentsMenuItem;
    private javax.swing.JMenuItem copyMenuItem;
    private javax.swing.JMenuItem cutMenuItem;
    private javax.swing.JMenuItem deleteMenuItem;
    private javax.swing.JMenu editMenu;
    private javax.swing.JMenuItem exitMenuItem;
    private javax.swing.JMenu fileMenu;
    private javax.swing.JMenu helpMenu;
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JScrollPane jScrollPane2;
    private javax.swing.JSplitPane jSplitPane1;
    private javax.swing.JTextPane jTextPane1;
    private javax.swing.JTree jTree1;
    private javax.swing.JMenuBar menuBar;
    private javax.swing.JMenuItem openMenuItem;
    private javax.swing.JMenuItem pasteMenuItem;
    private javax.swing.JMenuItem saveAsMenuItem;
    private javax.swing.JMenuItem saveMenuItem;
    private JPanel documentPanel = new JPanel();
    // End of variables declaration//GEN-END:variables
}

Here only two methods is written by me. All other codes are from PDFDebugger class of PDFBox