diff --git a/pdfbox/src/main/java/org/apache/pdfbox/cos/COSDocument.java b/pdfbox/src/main/java/org/apache/pdfbox/cos/COSDocument.java
index 0998f1a9b36..9f73947f614 100644
--- a/pdfbox/src/main/java/org/apache/pdfbox/cos/COSDocument.java
+++ b/pdfbox/src/main/java/org/apache/pdfbox/cos/COSDocument.java
@@ -485,6 +485,12 @@ public void close() throws IOException
         }
         closed = true;
 
+        // Release large data structures immediately so the GC can reclaim memory
+        // even if callers hold a reference to this COSDocument instance.
+        objectPool.clear();
+        xrefTable.clear();
+        trailer = null;
+
         // rethrow first exception to keep method contract
         if (firstException != null)
         {