Exception when using MergeDocument

I've encountered following exception, when loading pdfDocument into MergeDocument class:

System.InvalidCastException: Unable to cast object of type 'zz93.nw' to type 'zz93.oa'.
at ceTe.DynamicPDF.ViewerPreferences.a(n0 A_0, np A_1)
at zz93.n2.d(MergeDocument A_0, np A_1)\r\n   at zz93.nt.a(Int32 A_0, Int32 A_1)
at ceTe.DynamicPDF.Merger.MergeDocument..ctor(PdfDocument pdfDocument, MergeOptions options)
at InDoc.Document.Watermark.PdfWatermarker.AddWatermark(Stream documentStream, Options options)


The code that throws exception is:
var pdf = new PdfDocument(documentStream);
var mergeDocument = new MergeDocument(pdf);

Hello,

Can you please send over the following details to support@cete.com so we can look into it further?

1.Input PDF used for merging.
2.Code sample or project which uses static data to recreate the error.
3.Exact version and build number of the DynamicPDF DLL file used in the application. You can get this information in DLL references properties (version and Description fields) in Visual Studio.

Thanks,
ceTe Software Support Team.