System.NullReferenceException: Object reference not set to an instance of an object.
   at Telerik.Windows.Pdf.Documents.Fixed.FormatProviders.Old.Pdf.PdfElementToFixedElementTranslator.CreateFormField(PdfContentManager contentManager, FormFieldNodeOld terminalFormField)
   at Telerik.Windows.Pdf.Documents.Fixed.FormatProviders.Old.Pdf.PdfElementToFixedElementTranslator.CreateWidgetAnnotation(WidgetOld source, PdfFormatProvider provider)
   at Telerik.Windows.Pdf.Documents.Fixed.FormatProviders.Old.Pdf.PdfElementToFixedElementTranslator.CreateAnnotation(AnnotationOld source, PdfFormatProvider provider)
   at Telerik.Windows.Pdf.Documents.Fixed.FormatProviders.Pdf.PdfFormatProvider.CopyAnnotationsFromPageSource(PageOld source, AnnotationCollection annotations)
   at Telerik.Windows.Pdf.Documents.Fixed.FormatProviders.Pdf.PdfFormatProvider.LoadPageAnnotations(RadFixedPage page)
   at Telerik.Windows.Pdf.Documents.Fixed.Model.RadFixedPage.LoadAnnotations()
   at Telerik.Windows.Pdf.Documents.Fixed.Model.Internal.RadFixedPageInternal.Arrange()
   at Telerik.Windows.Pdf.Documents.Fixed.FormatProviders.Old.Pdf.PdfReader.PageContentLoader.Telerik.Windows.Pdf.Documents.Fixed.FormatProviders.Old.Pdf.PdfReader.IPageContentLoader.LoadPageContent(RadFixedPage page)
   at Telerik.Windows.Pdf.Documents.Fixed.FormatProviders.Old.Pdf.PdfReader.PagesCacheManager.BeginUsingPageContent(RadFixedPage page)
   at Telerik.WinControls.UI.RadFixedPageElement.Attach(RadFixedPage data, Object context)
   at Telerik.WinControls.UI.RadFixedPageElement..ctor(RadFixedPage page, RadPdfViewerElement owner)
   at Telerik.WinControls.UI.RadPdfViewerElement.CreatePageElement(RadFixedPage data, Object context)
   at Telerik.WinControls.UI.FixedPageElementProvider.CreateElement(RadFixedPage data, Object context)
   at Telerik.WinControls.UI.BaseVirtualizedElementProvider`1.GetElement(T data, Object context)
   at Telerik.WinControls.UI.BaseVirtualizedContainer`1.UpdateElement(Int32 position, T data)
   at Telerik.WinControls.UI.BaseVirtualizedContainer`1.MeasureElements()
   at Telerik.WinControls.PdfViewer.PdfViewerStackContainer.MeasureElements()
   at Telerik.WinControls.UI.BaseVirtualizedContainer`1.MeasureOverride(SizeF availableSize)
   at Telerik.WinControls.RadElement.MeasureCore(SizeF availableSize)
   at Telerik.WinControls.RadElement.Measure(SizeF availableSize)
   at Telerik.WinControls.UI.ScrollViewElement`1.MeasureViewElement(SizeF availableSize)
   at Telerik.WinControls.UI.ScrollViewElement`1.MeasureView(SizeF availableSize)
   at Telerik.WinControls.UI.ScrollViewElement`1.MeasureOverride(SizeF availableSize)
   at Telerik.WinControls.UI.VirtualizedScrollPanel`2.MeasureOverride(SizeF availableSize)
   at Telerik.WinControls.UI.RadPdfViewerElement.MeasureOverride(SizeF availableSize)
   at Telerik.WinControls.RadElement.MeasureCore(SizeF availableSize)
   at Telerik.WinControls.RadElement.Measure(SizeF availableSize)
   at Telerik.WinControls.Layouts.ContextLayoutManager.UpdateLayout()
   at Telerik.WinControls.Layouts.ContextLayoutManager.UpdateLayoutCallback(ILayoutManager manager)