Extract PdfPage coping excluded keys

SUP-3818

Author: pavel-alay

kernel/src/main/java/com/itextpdf/kernel/pdf/PdfPage.java

@@ -77,14 +77,25 @@ public class PdfPage extends PdfObjectWrapper<PdfDictionary> {
     private PdfResources resources = null;
     private int mcid = -1;
     PdfPages parentPages;
-    private List<PdfName> excludedKeys = new ArrayList<>(Arrays.asList(
+    private static final List<PdfName> PAGE_EXCLUDED_KEYS = new ArrayList<>(Arrays.asList(
             PdfName.Parent,
             PdfName.Annots,
             PdfName.StructParents,
             // This key contains reference to all articles, while this articles could reference to lots of pages.
             // See DEVSIX-191
             PdfName.B));
 
+    private static final List<PdfName> XOBJECT_EXCLUDED_KEYS;
+
+    static {
+        XOBJECT_EXCLUDED_KEYS = new ArrayList<>(Arrays.asList(PdfName.MediaBox,
+                PdfName.CropBox,
+                PdfName.TrimBox,
+                PdfName.Contents));
+        XOBJECT_EXCLUDED_KEYS.addAll(PAGE_EXCLUDED_KEYS);
+    }
+
+
     /**
      * Automatically rotate new content if the page has a rotation ( is disabled by default )
      */
@@ -377,7 +388,7 @@ public PdfPage copyTo(PdfDocument toDocument) {
      * @return copied {@link PdfPage}.
      */
     public PdfPage copyTo(PdfDocument toDocument, IPdfPageExtraCopier copier) {
-        PdfDictionary dictionary = getPdfObject().copyTo(toDocument, excludedKeys, true);
+        PdfDictionary dictionary = getPdfObject().copyTo(toDocument, PAGE_EXCLUDED_KEYS, true);
         PdfPage page = new PdfPage(dictionary);
         copyInheritedProperties(page, toDocument);
         for (PdfAnnotation annot : getAnnotations()) {
@@ -418,13 +429,9 @@ public PdfPage copyTo(PdfDocument toDocument, IPdfPageExtraCopier copier) {
      */
     public PdfFormXObject copyAsFormXObject(PdfDocument toDocument) throws IOException {
         PdfFormXObject xObject = new PdfFormXObject(getCropBox());
-        List<PdfName> excludedKeys = new ArrayList<>(Arrays.asList(PdfName.MediaBox,
-                PdfName.CropBox,
-                PdfName.Contents)
-        );
-        excludedKeys.addAll(this.excludedKeys);
+
         for (PdfName key : getPdfObject().keySet()) {
-            if (excludedKeys.contains(key)) {
+            if (XOBJECT_EXCLUDED_KEYS.contains(key)) {
                 continue;
             }
             PdfObject obj = getPdfObject().get(key);

kernel/src/main/java/com/itextpdf/kernel/pdf/xobject/PdfFormXObject.java

@@ -88,6 +88,9 @@ public PdfFormXObject(Rectangle bBox) {
      */
     public PdfFormXObject(PdfStream pdfStream) {
         super(pdfStream);
+        if (!getPdfObject().containsKey(PdfName.Subtype)) {
+            getPdfObject().put(PdfName.Subtype, PdfName.Form);
+        }
     }
 
     /**