The conversion of this XFA-Form PDF was running for almost 15 minutes.
Also the conversion output was not really great.
tmpA31F.pdf (89.6 KB)
Comparing the output to the original shows many differences.
XFA-Forms can be viewed with Adobe Reader DC, but not all PDF readers.
GroupDocs.Viewer 22.7 was used, without any special options:
    using (var viewer = new Viewer(documentPath))
    {   
        var options = HtmlViewOptions.ForEmbeddedResources("output_viewer{0}.html");
        viewer.View(options);
    }
Are XFA-Forms officially supported by GroupDocs?
I also tried with GroupDocs.Conversion, but that rendered an error page.