iText 7.0.5: How to combine PDF and have existing bookmarks indented under new bookmarks for each document?

Question

Problem: com.itextpdf.kernel.PdfException: Pdf indirect object belongs to other PDF document. Copy object to current pdf document.

I want to combine PDF documents with an edited set of bookmarks that keeps a clear pairing of the bookmarks with each original document. I also want a new top level bookmark describing the set as a whole to improve combining with yet other documents later if the user chooses. The number of documents combined and the number of bookmarks in each is unknown and some documents might not have any bookmarks.

For simplicity, assume I have two documents with two pages and a bookmark to the second page in each. I would want the combined document to have a bookmark structure like this where "NEW" are the ones I am creating based on meta data I have about each source document and "EXISTING" are whatever I copy from the individual documents:

-- NEW Combined Document meta(page 1)
---- NEW Document one meta   (page 1)
------ EXISTING Doc one link (page 2)
---- NEW Document two meta   (page 3)
------ EXISTING Doc two link (page 4)

Code:

private static String combinePdf(List<String> allFile, LinkedHashMap<String, String> bookmarkMetaMap, Connection conn) throws IOException {
System.out.println("=== combinePdf()  ENTER");  // TODO REMOVE
File outFile = File.createTempFile("combinePdf", "pdf", new File(DocumentObj.TEMP_DIR_ON_SERVER));
if (!outFile.exists() || !outFile.canWrite()) {
  throw new IOException("Unable to create writeable file in " + DocumentObj.TEMP_DIR_ON_SERVER);
}
if (bookmarkMetaMap == null || bookmarkMetaMap.isEmpty()) {
  bookmarkMetaMap = new LinkedHashMap<>(); // prevent NullPointer below
  bookmarkMetaMap.put("Documents", "Documents");
}
try ( PdfDocument allPdfDoc = new PdfDocument(new PdfWriter(outFile)) ) {
  allPdfDoc.initializeOutlines();
  allPdfDoc.getCatalog().setPageMode(PdfName.UseOutlines);
  PdfMerger allPdfMerger = new PdfMerger(allPdfDoc, true, false); // build own outline
  Iterator<Map.Entry<String, String>> itr = bookmarkMetaMap.entrySet().iterator();
  PdfOutline rootOutline = allPdfDoc.getOutlines(false);
  PdfOutline mainOutline;
  mainOutline = rootOutline.addOutline(itr.next().getValue());
  mainOutline.addDestination(PdfExplicitDestination.createFit(allPdfDoc.getNumberOfPages() + 1));
  int fileNum = 0;
  for (String oneFile : allFile) {
    PdfDocument onePdfDoc = new PdfDocument(new PdfReader(oneFile));
    PdfAcroForm oneForm = PdfAcroForm.getAcroForm(onePdfDoc, false);
    if (oneForm != null) {
      oneForm.flattenFields();
    }
    allPdfMerger.merge(onePdfDoc, 1, onePdfDoc.getNumberOfPages());
    fileNum++;
    String bookmarkLabel = itr.hasNext() ? itr.next().getKey() : "Document " + fileNum;
    PdfOutline linkToDoc = mainOutline.addOutline(bookmarkLabel);
    linkToDoc.addDestination(PdfExplicitDestination.createFit(allPdfDoc.getNumberOfPages() + 1));
    PdfOutline srcDocOutline = onePdfDoc.getOutlines(false);
    if (srcDocOutline != null) {
      List<PdfOutline> outlineList = srcDocOutline.getAllChildren();
      if (!outlineList.isEmpty()) {
        for (PdfOutline p : outlineList) {
          linkToDoc.addOutline(p);    // if I comment this out, no error, but links wrong order
        }
      }
    }
    onePdfDoc.close();
  }
  System.out.println("=== combinePdf()  DONE ADDING PAGES ===");    //TODO REMOVE
}
return outFile.getAbsolutePath();
}

Problem: com.itextpdf.kernel.PdfException: Pdf indirect object belongs to other PDF document. Copy object to current pdf document.

Error occurs after the debug line "=== combinePdf() DONE ADDING PAGES ===" so the for loop completes as expected. This means the error occurs when allPdfDoc is automagically closed. If I remove the line linkToDoc.addOutline(p); I get all of my links and they go to the correct pages but they are not nested/ordered as I want:

-- NEW Combined Document meta(page 1)
---- NEW Document one meta   (page 1)
---- NEW Document two meta   (page 3)
-- EXISTING Doc one link   (page 2)
-- EXISTING Doc two link   (page 4)

With the aforementioned line commented out, I am not even sure how the EXISTING links are included at all. I have the mergeOutlines flag set to false in the PdfMerger constructor since I thought I had to construct my own outline. I get similar results no matter whether I set the getOutlines() to true or false as well as if I take out my arbitrary top level new bookmark.

I know how to create a flattened list of new and existing bookmarks in the desired order. So my question is about how to get both the indenting and ordering as desired.

Thanks for taking a look!

Answer 1

Rather than shift bookmarks in the combined PDF, I did it in the component PDF before merging. Feedback welcome, especially if something is horribly inefficient as PDF size increases:

private static void shiftPdfBookmarksUnderNewBookmark(PdfDocument pdfDocument, String bookmarkLabel) {
if (pdfDocument == null || pdfDocument.getWriter() == null) {
  log.warn("shiftPdfBookmarksUnderNewBookmark(): no writer linked to PDFDocument, cannot modify bookmarks");
  return;
}
pdfDocument.initializeOutlines();
try {
  PdfOutline rootOutline = pdfDocument.getOutlines(false);
  PdfOutline subOutline = rootOutline.addOutline(bookmarkLabel);
  subOutline.addDestination(PdfExplicitDestination.createFit(pdfDocument.getFirstPage())); // Not sure why this is needed, but problems if omitted.
  List<PdfOutline> pdfOutlineChildren = rootOutline.getAllChildren();
  if (pdfOutlineChildren.size() == 1) {
    return;
  }
  int i = 0;
  for (PdfOutline p : rootOutline.getAllChildren()) {
    if (p != subOutline) {
      if (p.getDestination() == null) {
        continue;
      }
      subOutline.addOutline(p);
    }
  }
  rootOutline.getAllChildren().clear();
  rootOutline.addOutline(subOutline);
  subOutline.addDestination(PdfExplicitDestination.createFit(pdfDocument.getFirstPage())); // not sure why duplicate line above seems to be needed
}
catch (Exception logAndIgnore) {
  log.warn("shiftPdfBookmarksUnderNewBookmark ignoring error and not shifting bookmarks: " +logAndIgnore, logAndIgnore);
}
}