Fix PdfAcroform flattening bug with circular references when xObject's resources and page resources are a same object and we later want to add xObject to the page resources

Author: Snipx

core/src/main/java/com/itextpdf/core/pdf/PdfObject.java

@@ -215,7 +215,7 @@ public PdfDocument getDocument() {
      * @return cloned object.
      */
     @Override
-    public Object clone() {
+    public PdfObject clone() {
         PdfObject newObject = newInstance();
         if (indirectReference != null || checkState(MustBeIndirect)) {
             newObject.setState(MustBeIndirect);

forms/src/main/java/com/itextpdf/forms/PdfAcroForm.java

@@ -565,6 +565,17 @@ public void flattenFields() {
             }
         }
 
+        // In case of appearance resources and page resources are the same object, it would not be possible to add
+        // the xObject to the page resources. So in that case we would copy page resources and use the copy for
+        // xObject, so that circular reference is avoided.
+        // We copy beforehand firstly not to produce a copy every time, and secondly not to copy all the
+        // xObjects that have already been added to the page resources.
+        Map<Integer, PdfObject> initialPageResourceClones = new LinkedHashMap<>();
+        for (int i = 1; i <= document.getNumberOfPages(); i++) {
+            PdfObject resources = document.getPage(i).getPdfObject().getAsDictionary(PdfName.Resources);
+            initialPageResourceClones.put(i, resources == null ? null : resources.clone());
+        }
+
         PdfPage page;
         for (PdfFormField field : fields) {
             page = getFieldPage(field.getPdfObject());
@@ -604,6 +615,16 @@ public void flattenFields() {
                         throw new PdfException(PdfException.PageWasAlreadyFlushedUseAddFieldAppearanceToPageMethodInstead);
                     }
                     PdfCanvas canvas = new PdfCanvas(page);
+
+                    // Here we avoid circular reference which might occur when page resources and the appearance xObject's
+                    // resources are the same object
+                    PdfObject xObjectResources = xObject.getPdfObject().get(PdfName.Resources);
+                    PdfObject pageResources = page.getResources().getPdfObject();
+                    if (xObjectResources != null && pageResources != null &&
+                            xObjectResources == pageResources) {
+                        xObject.getPdfObject().put(PdfName.Resources, initialPageResourceClones.get(document.getPageNumber(page)));
+                    }
+                    
                     canvas.addXObject(xObject, box.getX(), box.getY());
                 }
             }

forms/src/main/java/com/itextpdf/forms/fields/PdfFormField.java

@@ -409,6 +409,8 @@ public static PdfChoiceFormField createChoice(PdfDocument doc, Rectangle rect, S
     public static PdfChoiceFormField createChoice(PdfDocument doc, Rectangle rect, String name, String value, PdfFont font, int fontSize, PdfArray options, int flags) {
         PdfWidgetAnnotation annot = new PdfWidgetAnnotation(rect);
         PdfChoiceFormField field = new PdfChoiceFormField(annot, doc);
+        field.font = font;
+        field.fontSize = fontSize;
         field.put(PdfName.Opt, options);
         field.setFieldFlags(flags);
         field.setFieldName(name);