Discussion

The Atalasoft WPF Annotation Viewer (AtalaAnnotationViewer class)  attempts to extract annotations embedded in PDFs by default.

If you wish to disable this feature entirely you can set

atalaAnnotationViewer1.AutoImportXmp = false;

However, you may want to import annotations embedded in PDF but ignore unknown annotation types. The default behavior is that unknown annotation types will be rendered as WpfTextAnnotation with the text "Unknown Annotation" which can be very annoying.

In theory, one should be able to disable the import of unknown types simply by enumerating the AtalaAnnotationViewer.Importers until you find the PdfAnnotationDataImporter and set its SkipUnknownAnnotationTypes property to true

However, this setting has no effect...

The root cause is due to a slight design oversight of how we need to use the importers in the WPF viewer

The fix is to derive a custom PdfAnnotationDataImporter that implements the missing pieces and replace the current importer

Implementation Example

First, add this custom PdfAnnotationDataImporter class to your project

public class CustomPdfAnnotationDataImporter:PdfAnnotationDataImporter
{
    public override AnnotationDataImporter FromStream(Stream stm)
    {
        var importer = base.FromStream(stm);
        if (importer is PdfAnnotationDataImporter pdfAnnotationDataImporter)
        {
            pdfAnnotationDataImporter.SkipUnknownAnnotationTypes = SkipUnknownAnnotationTypes;
            pdfAnnotationDataImporter.FailsafeAnnotationFactory = FailsafeAnnotationFactory;
        }
        return importer;
    }
}

Second, instantiate a new CustomPdfAnnotationDataImporter, clear the Importers collection and add this new importer

In this example. your AtalaAnnotationViewer is named atalaAnnotationViewer1

var importer = new CustomPdfAnnotationDataImporter
{
    SkipUnknownAnnotationTypes = true
};

this.atalaAnnotationViewer1.Importers.Clear();
this.atalaAnnotationViewer1.Importers.Add(importer);