PDFBOX-6058: Preserve Perms dictionary when signing

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/trunk@1928170 13f79535-47bb-0310-9956-ffa450edef68

Author: THausherr

examples/src/main/java/org/apache/pdfbox/examples/signature/SigUtils.java

@@ -184,8 +184,12 @@ public static void setMDPPermission(PDDocument doc, PDSignature signature, int a
 
         // Catalog
         COSDictionary catalogDict = doc.getDocumentCatalog().getCOSObject();
-        COSDictionary permsDict = new COSDictionary();
-        catalogDict.setItem(COSName.PERMS, permsDict);
+        COSDictionary permsDict = catalogDict.getCOSDictionary(COSName.PERMS);
+        if (permsDict == null)
+        {
+            permsDict = new COSDictionary();
+            catalogDict.setItem(COSName.PERMS, permsDict);
+        }
         permsDict.setItem(COSName.DOCMDP, signature);
         catalogDict.setNeedToBeUpdated(true);
         permsDict.setNeedToBeUpdated(true);