I have a simple program that imports a PDF, calls AcroForm.FlattenFormFields(), and calls Export() on the PdfFormatProvider. I am seeing the following exception during Import() on a signed W9 form a customer has uploaded into our system. Due to the sensitive nature of the document I cannot upload it, but below is the Sig section. I have tried other example signed PDFs which seem to work fine (See attached)

39 0 obj
<< /Type /Annot /Rotate 0 /AP 180 0 R /Rect [ 105.8515 149.2023 289.4443 261.1185
] /Border [ 0 0 0 ] /M (h<D[×¥\001.ƒ¶AB}«\006iÚ¿E@\024_”W±ÔÃ\030ÙL\020"É]a\012Ú6¡0\000¶Žm1@Ž)
/C [ 1 ] /DA (h<D[×¥\001.ƒ¶AB}«\006.\023âø‰\035\005íöu\002ÊÒ½ùwË@—‹måÿڏ[ ‹í!¨\001)
/F 4 /Subtype /Sig >>
endobj

Exception

System.NotSupportedException: 'Import of annotation with type Sig is not supported.'

Stack Trace

at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.Annotations.AnnotationFactory.CreateUnsupportedAnnotationObject(PdfName type)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Converters.TypeAwareConverter`1.CreateInstance(Type type, PostScriptReader reader, IPdfImportContext context, PdfDictionary dictionary)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Converters.Converter.ConvertFromDictionary(Type type, PostScriptReader reader, IPdfImportContext context, PdfDictionary dictionary)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Converters.Converter.Convert(Type type, PostScriptReader reader, IPdfImportContext context, IPdfPrimitive value)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Converters.Converter.Convert(Type type, PostScriptReader reader, IPdfImportContext context, IPdfPrimitive value)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Types.PdfCollectionBase`1.ConvertElementToType[T](PostScriptReader reader, IPdfImportContext context, IPdfPrimitive element)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Types.PdfCollectionBase`1.TryGetElement[T](PostScriptReader reader, IPdfImportContext context, TIndex index, T& element)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.DocumentStructure.Page.<>c__DisplayClass21_0.<CopyPageAnnotationsTo>b__0()
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.ExceptionHandling.ExecutionHandler.TryHandleExecution[E](Action operation)