itextpdf.jar is a component in iText 5 Java library to provide core functionalities. iText Java library allows you to generate and manage PDF documents.

The Source Code files are provided at iText GitHub site.

You can compile it to generate your JAR file, using pom.xml as the build configuration file.

The source code of itextpdf-5.5.14.jar is provided below:

⏎ com/itextpdf/text/pdf/PdfPages.java

/*
 *
 * This file is part of the iText (R) project.
    Copyright (c) 1998-2020 iText Group NV
 * Authors: Bruno Lowagie, Paulo Soares, et al.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License version 3
 * as published by the Free Software Foundation with the addition of the
 * following permission added to Section 15 as permitted in Section 7(a):
 * FOR ANY PART OF THE COVERED WORK IN WHICH THE COPYRIGHT IS OWNED BY
 * ITEXT GROUP. ITEXT GROUP DISCLAIMS THE WARRANTY OF NON INFRINGEMENT
 * OF THIRD PARTY RIGHTS
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU Affero General Public License for more details.
 * You should have received a copy of the GNU Affero General Public License
 * along with this program; if not, see http://www.gnu.org/licenses or write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA, 02110-1301 USA, or download the license from the following URL:
 * http://itextpdf.com/terms-of-use/
 *
 * The interactive user interfaces in modified source and object code versions
 * of this program must display Appropriate Legal Notices, as required under
 * Section 5 of the GNU Affero General Public License.
 *
 * In accordance with Section 7(b) of the GNU Affero General Public License,
 * a covered work must retain the producer line in every PDF that is created
 * or manipulated using iText.
 *
 * You can be released from the requirements of the license by purchasing
 * a commercial license. Buying such a license is mandatory as soon as you
 * develop commercial activities involving the iText software without
 * disclosing the source code of your own applications.
 * These activities include: offering paid services to customers as an ASP,
 * serving PDFs on the fly in a web application, shipping iText with a closed
 * source product.
 *
 * For more information, please contact iText Software Corp. at this
 * address: sales@itextpdf.com
 */
package com.itextpdf.text.pdf;

import java.io.IOException;
import java.util.ArrayList;

import com.itextpdf.text.DocumentException;
import com.itextpdf.text.ExceptionConverter;
import com.itextpdf.text.error_messages.MessageLocalization;

/**
 * <CODE>PdfPages</CODE> is the PDF Pages-object.
 * <P>
 * The Pages of a document are accessible through a tree of nodes known as the Pages tree.
 * This tree defines the ordering of the pages in the document.<BR>
 * This object is described in the 'Portable Document Format Reference Manual version 1.3'
 * section 6.3 (page 71-73)
 *
 * @see		PdfPage
 */

public class PdfPages {

    private ArrayList<PdfIndirectReference> pages = new ArrayList<PdfIndirectReference>();
    private ArrayList<PdfIndirectReference> parents = new ArrayList<PdfIndirectReference>();
    private int leafSize = 10;
    private PdfWriter writer;
    private PdfIndirectReference topParent;

    // constructors

/**
 * Constructs a <CODE>PdfPages</CODE>-object.
 */

    PdfPages(PdfWriter writer) {
        this.writer = writer;
    }

    void addPage(PdfDictionary page) {
        try {
            if (pages.size() % leafSize == 0)
                parents.add(writer.getPdfIndirectReference());
            PdfIndirectReference parent = parents.get(parents.size() - 1);
            page.put(PdfName.PARENT, parent);
            PdfIndirectReference current = writer.getCurrentPage();
            writer.addToBody(page, current);
            pages.add(current);
        }
        catch (Exception e) {
            throw new ExceptionConverter(e);
        }
    }

    PdfIndirectReference addPageRef(PdfIndirectReference pageRef) {
        try {
            if (pages.size() % leafSize == 0)
                parents.add(writer.getPdfIndirectReference());
            pages.add(pageRef);
            return parents.get(parents.size() - 1);
        }
        catch (Exception e) {
            throw new ExceptionConverter(e);
        }
    }

    // returns the top parent to include in the catalog
    PdfIndirectReference writePageTree() throws IOException {
        if (pages.isEmpty())
            throw new IOException(MessageLocalization.getComposedMessage("the.document.has.no.pages"));
        int leaf = 1;
        ArrayList<PdfIndirectReference> tParents = parents;
        ArrayList<PdfIndirectReference> tPages = pages;
        ArrayList<PdfIndirectReference> nextParents = new ArrayList<PdfIndirectReference>();
        while (true) {
            leaf *= leafSize;
            int stdCount = leafSize;
            int rightCount = tPages.size() % leafSize;
            if (rightCount == 0)
                rightCount = leafSize;
            for (int p = 0; p < tParents.size(); ++p) {
                int count;
                int thisLeaf = leaf;
                if (p == tParents.size() - 1) {
                    count = rightCount;
                    thisLeaf = pages.size() % leaf;
                    if (thisLeaf == 0)
                        thisLeaf = leaf;
                }
                else
                    count = stdCount;
                PdfDictionary top = new PdfDictionary(PdfName.PAGES);
                top.put(PdfName.COUNT, new PdfNumber(thisLeaf));
                PdfArray kids = new PdfArray();
                ArrayList<PdfObject> internal = kids.getArrayList();
                internal.addAll(tPages.subList(p * stdCount, p * stdCount + count));
                top.put(PdfName.KIDS, kids);
                if (tParents.size() > 1) {
                    if (p % leafSize == 0)
                        nextParents.add(writer.getPdfIndirectReference());
                    top.put(PdfName.PARENT, nextParents.get(p / leafSize));
                }
                writer.addToBody(top, tParents.get(p));
            }
            if (tParents.size() == 1) {
                topParent = tParents.get(0);
                return topParent;
            }
            tPages = tParents;
            tParents = nextParents;
            nextParents = new ArrayList<PdfIndirectReference>();
        }
    }

    PdfIndirectReference getTopParent() {
        return topParent;
    }

    void setLinearMode(PdfIndirectReference topParent) {
        if (parents.size() > 1)
            throw new RuntimeException(MessageLocalization.getComposedMessage("linear.page.mode.can.only.be.called.with.a.single.parent"));
        if (topParent != null) {
            this.topParent = topParent;
            parents.clear();
            parents.add(topParent);
        }
        leafSize = 10000000;
    }

    void addPage(PdfIndirectReference page) {
        pages.add(page);
    }

    int reorderPages(int order[]) throws DocumentException {
        if (order == null)
            return pages.size();
        if (parents.size() > 1)
            throw new DocumentException(MessageLocalization.getComposedMessage("page.reordering.requires.a.single.parent.in.the.page.tree.call.pdfwriter.setlinearmode.after.open"));
        if (order.length != pages.size())
            throw new DocumentException(MessageLocalization.getComposedMessage("page.reordering.requires.an.array.with.the.same.size.as.the.number.of.pages"));
        int max = pages.size();
        boolean temp[] = new boolean[max];
        for (int k = 0; k < max; ++k) {
            int p = order[k];
            if (p < 1 || p > max)
                throw new DocumentException(MessageLocalization.getComposedMessage("page.reordering.requires.pages.between.1.and.1.found.2", String.valueOf(max), String.valueOf(p)));
            if (temp[p - 1])
                throw new DocumentException(MessageLocalization.getComposedMessage("page.reordering.requires.no.page.repetition.page.1.is.repeated", p));
            temp[p - 1] = true;
        }
        PdfIndirectReference copy[] = pages.toArray(new PdfIndirectReference[pages.size()]);
        for (int k = 0; k < max; ++k) {
            pages.set(k, copy[order[k] - 1]);
        }
        return max;
    }
}

⏎ com/itextpdf/text/pdf/PdfPages.java

Or download all of them as a single archive file:

File name: itextpdf-5.5.14-fyi.zip
File size: 2163839 bytes
Release date: 2009-10-09
Download 

⇒ iText-2.1.6.jar - iText, a JAVA-PDF library

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⇑ Download and Install iText Java Library

⇑⇑ iText for PDF Generation