Java PDFClown：如何克隆页面

我想在pdfclown的帮助下将旧pdf文件中的页面复制到新文件中

到目前为止，我尝试了以下方法：

    File newFile = new File();
    Document document = newFile.getDocument();
    for (int pageNumber : pageNumbers) {
         document.getPages().add(oldFile.getDocument().getPages().get(pageNumber).clone(document));
    }

    return newFile;

不幸的是，在执行

克隆（文档）

---

这种情况是针对每个源文档还是针对特定文档？如果您不确定，或者这只发生在特定的情况下，请共享一个发生这种情况的示例PDF。很抱歉我的回复太晚。我测试了不同的文件，似乎无法将包含

org.pdfclown.documents.interaction.annotations.Rectangle

的复制页面从旧文件传输到新文件。在这种情况下，请共享发生这种情况的示例PDF。

    java.lang.NullPointerException
    at org.pdfclown.files.IndirectObjects.addExternal(IndirectObjects.java:208)
    at org.pdfclown.objects.Cloner.visit(Cloner.java:357)
    at org.pdfclown.objects.Cloner.visit(Cloner.java:367)
    at org.pdfclown.objects.PdfReference.accept(PdfReference.java:94)
    at org.pdfclown.objects.Cloner.visit(Cloner.java:343)
    at org.pdfclown.objects.PdfDictionary.accept(PdfDictionary.java:161)
    at org.pdfclown.files.IndirectObjects.addExternal(IndirectObjects.java:208)
    at org.pdfclown.objects.Cloner.visit(Cloner.java:357)
    at org.pdfclown.objects.Cloner.visit(Cloner.java:367)
    at org.pdfclown.objects.PdfReference.accept(PdfReference.java:94)
    at org.pdfclown.objects.Cloner.visit(Cloner.java:318)
    at org.pdfclown.objects.PdfArray.accept(PdfArray.java:113)
    at org.pdfclown.files.IndirectObjects.addExternal(IndirectObjects.java:208)
    at org.pdfclown.objects.Cloner.visit(Cloner.java:357)
    at org.pdfclown.objects.Cloner.visit(Cloner.java:367)
    at org.pdfclown.objects.PdfReference.accept(PdfReference.java:94)
    at org.pdfclown.objects.Cloner.visit(Cloner.java:343)
    at org.pdfclown.objects.PdfDictionary.accept(PdfDictionary.java:161)
    at org.pdfclown.files.IndirectObjects.addExternal(IndirectObjects.java:208)
    at org.pdfclown.objects.Cloner.visit(Cloner.java:357)
    at org.pdfclown.objects.Cloner.visit(Cloner.java:367)
    at org.pdfclown.objects.PdfReference.accept(PdfReference.java:94)
    at org.pdfclown.objects.PdfObject.clone(PdfObject.java:96)
    at org.pdfclown.objects.PdfReference.clone(PdfReference.java:222)
    at org.pdfclown.objects.PdfReference.clone(PdfReference.java:1)
    at org.pdfclown.objects.PdfObjectWrapper.clone(PdfObjectWrapper.java:159)