What Is fop.jar? I got it from the fop-2.7-bin.zip.

fop.jar in fop-2.7-bin.zip is the JAR file for FOP 2.7, which is a print formatter driven by XSL formatting objects (XSL-FO). You can obtain fop.jar from the build folder of the fop-2.7-bin.zip file.

Below is the information about the fop.jar (2.2) file:

JAR File Size and Download Location:

JAR name: fop.jar, fop-2.7.jar
Target JDK version: 1.7
File name: fop.jar
File size: 4442817 bytes
Release date: 20-Jan-2022
Download: Apache FOP Website

Java source code files for fop.jar:

⏎ org/apache/fop/pdf/PDFStructTreeRoot.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/* $Id: PDFStructTreeRoot.java 1376923 2012-08-24 14:10:39Z vhennebert $ */

package org.apache.fop.pdf;

/**
 * Class representing a PDF /StructTreeRoot dictionary.
 */
public class PDFStructTreeRoot extends StructureHierarchyMember {

    /**
     * Creates a new /StructTreeRoot dictionary.
     *
     * @param parentTree the value of the ParenTree entry
     */
    PDFStructTreeRoot(PDFParentTree parentTree) {
        put("Type", new PDFName("StructTreeRoot"));
        put("K", new PDFArray());
        put("ParentTree", parentTree);
    }

    /**
     * Returns the children element of this StructTreeRoot.
     *
     * @return the value of the K entry
     */
    public PDFArray getKids() {
        return (PDFArray)get("K");
    }

    /**
     * Adds the given object to the array of kids.
     *
     * @param kid an object to be added to the K entry
     */
    @Override
    public void addKid(PDFObject kid) {
        getKids().add(kid);
    }
}

⏎ org/apache/fop/pdf/PDFStructTreeRoot.java

Or download all of them as a single archive file:

File name: fop-2.7-src.zip
File size: 3401312 bytes
Release date: 2022-01-20
Download 

⇒ "fop" Command in fop-2.7-bin.zip

⇐ What Is fop-2.7-bin.zip

⇑ Download and Installing of FOP 2.x

⇑⇑ FAQ for FOP (Formatting Object Processor)