From 92456710eecabdc2cf6400e37c660e42a04b5c31 Mon Sep 17 00:00:00 2001
From: Bernhard Fey <43403851+bernhardf-ro@users.noreply.github.com>
Date: Tue, 10 Jan 2023 12:32:44 +0100
Subject: [PATCH] Allow negative struct parent keys in PDFMergerUtility

PDFMergerUtility expects structural parent tree keys to be non-negative.
However, negative values don't seem to be forbidden by the specification and are accepted by validators.
This patch adapts the class to handle negative struct parent keys correctly.
---
 .../java/org/apache/pdfbox/multipdf/PDFMergerUtility.java    | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/pdfbox/src/main/java/org/apache/pdfbox/multipdf/PDFMergerUtility.java b/pdfbox/src/main/java/org/apache/pdfbox/multipdf/PDFMergerUtility.java
index ea5d9cd0807..86997c347f7 100644
--- a/pdfbox/src/main/java/org/apache/pdfbox/multipdf/PDFMergerUtility.java
+++ b/pdfbox/src/main/java/org/apache/pdfbox/multipdf/PDFMergerUtility.java
@@ -795,6 +795,7 @@ else if (destOCP != null && srcOCP != null)
                         if (!srcNumberTreeAsMap.isEmpty())
                         {
                             mergeStructTree = true;
+                            destParentTreeNextKey -= Collections.min(srcNumberTreeAsMap.keySet()); // allow for negative struct parent values
                         }
                     }
                 }
@@ -1498,8 +1499,8 @@ private void updateStructParentEntries(PDPage page, int structParentOffset) thro
         List<PDAnnotation> newannots = new ArrayList<>(annots.size());
         annots.forEach(annot ->
         {
-            int structParent = annot.getStructParent();
-            if (structParent >= 0)
+            int structParent = annot.getCOSObject().getInt(COSName.STRUCT_PARENT, Integer.MIN_VALUE); // allow for negative struct parent values
+            if (structParent > Integer.MIN_VALUE) // allow for negative struct parent values
             {
                 annot.setStructParent(structParent + structParentOffset);
             }