How to merge PDFs and add bookmarks?

I am merging multiple PDFs together into one PDF and I need to build bookmarks for the final PDF. For example, I have three PDFs: doc1.pdf, doc2.pdf and doc3.pdf, doc1 and doc2 belong to Group1, doc3 belongs to Group2. I need to merge them and have to build nested bookmarks for the resulting PDFs like this:

Group1
    doc1
    doc2
Group2
    doc3

Posted on StackOverflow on May 15, 2014 by user3642526

I've made a MergeWithOutlines example that concatenates three existing PDFs using PdfCopy (I assume that you already know that part).

While doing so, I create an outlines object like this:

ArrayList> outlines = new ArrayList>();

and I add elements to this outlines object:

HashMap helloworld = new HashMap();
helloworld.put("Title", "Hello World");
helloworld.put("Action", "GoTo");
helloworld.put("Page", String.format("%d Fit", page));
outlines.add(helloworld);

When I want some hierarchy, I introduce kids:

ArrayList> kids = new ArrayList>();
HashMap link1 = new HashMap();
link1.put("Title", "link1");
link1.put("Action", "GoTo");
link1.put("Page", String.format("%d Fit", page));
kids.add(link1);
helloworld.put("Kids", kids);

If you want an entry without a link, remove the lines that put an Action and a Page.

Once you're finished, add the outlines to the copy object:

copy.setOutlines(outlines);

Look at the resulting PDF and you'll see the outlines in the bookmarks panel.

Click this link if you want to see how to answer this question in iText 7.