How to create a TOC when merging documents?

I need to create a TOC (not bookmarks) at the beginning of this document with clickable links to the first pages of each of the source PDFs.

Document document = new Document();
PdfCopy copy = new PdfCopy(document, outputStream);
PdfCopy.PageStamp stamp;
document.open();
PdfReader reader;
<ListInputStream> pdfs = streamOfPDFFiles;
<ListPdfReader> readers = new ArrayListPdfReader>();
<IteratorInputStream> iteratorPDFs = pdfs.iterator();
for (; iteratorPDFs.hasNext(); pdfCounter++) {
    InputStream pdf = iteratorPDFs.next();
    reader = new PdfReader(pdf);
    readers.add(reader);
    pdf.close();
}
int currentPageNumber = 0;
<IteratorPdfReader> readerIterator = readers.iterator();
PdfImportedPage page;
int count = 1;
while (readerIterator.hasNext()) {
    reader = readerIterator.next();
    count++;
    int number_of_pages = reader.getNumberOfPages();
    for (int pageNum = 0; pageNum  number_of_pages;) {
        currentPageNumber++;
        page = copy.getImportedPage(reader, ++pageNum);
        ColumnText.showTextAligned(stamp.getUnderContent(),
            Element.ALIGN_RIGHT, new Phrase(
                String.format("%d", currentPageNumber),
                new Font(FontFamily.TIMES_ROMAN,3)), 50, 50, 0);
        stamp.alterContents();
        copy.addPage(page);
    }
}
document.close();

You're asking for something that should be trivial, but that isn't. Please take a look at the MergeWithToc example. You'll see that your code to merge PDFs is correct, but in my example, I added one extra feature:

chunk = new Chunk(String.format("Page %d", pageNo));
if (i == 1)
    chunk.setLocalDestination("p" + pageNo);
ColumnText.showTextAligned(stamp.getUnderContent(),
    Element.ALIGN_RIGHT, new Phrase(chunk), 559, 810, 0);

For every first page, I define a named destination as a local destination. We use p followed by the page number as its name.

We'll use these named destinations in an extra page that will serve as a TOC:

PdfReader reader = new PdfReader(SRC3);
page = copy.getImportedPage(reader, 1);
stamp = copy.createPageStamp(page);
Paragraph p;
PdfAction action;
PdfAnnotation link;
float y = 770;
ColumnText ct = new ColumnText(stamp.getOverContent());
ct.setSimpleColumn(36, 36, 559, y);
for (Map.Entry entry : toc.entrySet()) {
    p = new Paragraph(entry.getValue());
    p.add(new Chunk(new DottedLineSeparator()));
    p.add(String.valueOf(entry.getKey()));
    ct.addElement(p);
    ct.go();
    action = PdfAction.gotoLocalPage("p" + entry.getKey(), false);
    link = new PdfAnnotation(copy, 36, ct.getYLine(), 559, y, action);
    stamp.addAnnotation(link);
    y = ct.getYLine();
}
ct.go();
stamp.alterContents();
copy.addPage(page);

In my example, I assume that the TOC fits on a single page. You'll have to keep track of the y value and create a new page if its value is lower than the bottom margin.

If you want the TOC to be the first page, you need to reorder the pages in a second go. This is shown in the MergeWithToc2 example:

reader = new PdfReader(baos.toByteArray());
n = reader.getNumberOfPages();
reader.selectPages(String.format("%d, 1-%d", n, n-1));
PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(filename));
stamper.close();