Document.Save Exception when modifying page

I am attempting to append text (htmlfragment) to the bottom of a page in a PDF file, however after adding the HTMLFragement, calls to save throw an exception. The code is:

    Aspose.Pdf.Document pdfDoc = new Aspose.Pdf.Document(WorkingFile + ".pdf");
    pdfDoc.Pages[1].Paragraphs.Add(new Aspose.Pdf.HtmlFragment("<p>anything</p>"));
    pdfDoc.Save(WorkingFile + ".notes.pdf", Aspose.Pdf.SaveFormat.Pdf);

Working File 00003015.PPT.pdf (575.2 KB)
Is attached to the ticket.

Exception Details:
‘pdfDoc.Save(WorkingFile + “.notes.pdf”, Aspose.Pdf.SaveFormat.Pdf)’ threw an exception of type ‘System.NullReferenceException’
Data: {System.Collections.ListDictionaryInternal}
HResult: -2147467261
HelpLink: null
InnerException: null
Message: “Object reference not set to an instance of an object.”
Source: “Aspose.Pdf”
StackTrace: " at Aspose.Pdf.FormattedFragment.\u0002(Page \u0002, Page \u0003)\r\n at \u0005 .\b \u0002(SizeF \u0002)\r\n at \u0006 .\b \u0002(SizeF \u0002)\r\n at \u0005 .\u0005 \u0002(\u0002 \u0002)\r\n at \b .\u0005 \u0002(\u0005 [] \u0002, \b \u0003)\r\n at \u000f​ .\u000e \u0002(\b \u0002, \b \u0003)\r\n at Aspose.Pdf.FormattedFragment.\u0002(Double& \u0002, Double& \u0003, Boolean \u0005, Double \b, Double \u0006, List`1 \u000e, Page \u000f, MarginInfo \u0002 , Table \u0003 )\r\n at \u000e .\u0005()\r\n at Aspose.Pdf.Page.\u0003(Page \u0002)\r\n at Aspose.Pdf.Document.ProcessParagraphs()\r\n at Aspose.Pdf.Document.Save(Stream output)\r\n at Aspose.Pdf.Document.Save(Stream outputStream, SaveOptions options)\r\n at Aspose.Pdf.Document.Save(String outputFileName, SaveFormat format)"
TargetSite: {Void (Aspose.Pdf.Page, Aspose.Pdf.Page)}

@enierman

Thank you for contacting support.

I have worked with the data shared by you and have been able to reproduce the issue in our environment. A ticket with ID PDFNET-43876* has been logged in our issue management system for further investigation and resolution. The issue ID has been linked with this thread so that you will receive notification as soon as the issue is resolved.

We are sorry for the inconvenience.

The issues you have found earlier (filed as PDFNET-43876) have been fixed in Aspose.PDF for .NET 21.2.