Error: Unable to cast object of type 'zz93.ek' to type 'zz93.ey'

Hello, my company use Merger 7.0.2.40 for attach footer to document.
We have problem with few documents.

Problem source:
    var source  = new PdfDocument(src);
    var doc     = new MergeDocument(source, new MergeOptions {XmpMetadata = false});

Error message (v.7.0.2.40):
System.InvalidCastException : Unable to cast object of type 'zz93.ek' to type 'zz93.ey'.
   at ceTe.DynamicPDF.ViewerPreferences.a(eo A_0, ec A_1)
   at zz93.eq.b(MergeDocument A_0, ec A_1)
   at ceTe.DynamicPDF.Merger.PdfDocument.b(MergeDocument A_0, ec A_1)
   at zz93.f6.a(Int32 A_0, Int32 A_1)
   at ceTe.DynamicPDF.Merger.MergeDocument.a(PdfDocument A_0, Int32 A_1, Int32 A_2, f6 A_3, Boolean A_4)
   at ceTe.DynamicPDF.Merger.MergeDocument.a(PdfDocument A_0, f6 A_1, Boolean A_2)
   at ceTe.DynamicPDF.Merger.MergeDocument..ctor(PdfDocument pdfDocument, MergeOptions options)
   at _confidential_.WriteFooter(Stream src, Stream dst, PdfFooterDto footerInfo)

Also, we tried version 11.3.0.42707 and reach a similar error:
 System.InvalidCastException : Unable to cast object of type 'zz93.abj' to type 'zz93.aby'.
   at ceTe.DynamicPDF.ViewerPreferences.a(abn A_0)
   at zz93.abp.e(MergeDocument A_0)
   at ceTe.DynamicPDF.Merger.PdfDocument.a(MergeDocument A_0)
   at zz93.abf.a(Int32 A_0, Int32 A_1)
   at ceTe.DynamicPDF.Merger.MergeDocument.a(PdfDocument A_0, abf A_1, Boolean A_2)
   at ceTe.DynamicPDF.Merger.MergeDocument..ctor(PdfDocument pdfDocument, MergeOptions options)
   at _confidential_.WriteFooter(Stream src, Stream dst, PdfFooterDto footerInfo)
  
Unfortunately, all documents that cause this error contain confidential information and cannot be attached.
Is it possible to get fix for version 7.0.2?

Hello,

v7 has reached end of life (the current version is v11), so there is a good chance we won't be able to provide an update for that version. Also please send over the following information to support@dynamicpdf.com  so we can look into it further.

1.        Source PDFs for which you are getting the error.
2.        Code sample used.
3.        Full error message along with stack trace.
4.        Exact version and build number of the DynamicPDF DLL file used in the application. You can find this information in DLL references properties (Version and Description fields) in Visual Studio.

Thanks,
ceTe Software Support Team