Java Lambda Expression to C# Translation

I am currently trying to convert this piece of Java, which contains Lambda Expressions (.stream(), .filter(), collect() methods) code to C# LINQ code:

Java Code:

        Map<Rectangle, PdfStream> highlightStreams = page.getAnnotations()
            .stream()
            .filter((a) -> (PdfName.Stamp.equals(a.getSubtype()) || PdfName.FreeText.equals(a.getSubtype())) && a.getNormalAppearanceObject().isStream())
            .collect(
                    Collectors.toMap(
                            a -> a.getRectangle().toRectangle(),
                            a -> (PdfStream) a.getNormalAppearanceObject()
                    ));
    page.getAnnotations().forEach(page::removeAnnotation);

Here is the C# that I have so far. Some of the API classes are from iText7. I would like some help on it if possible please on how this can be translated to C#.

C# Code:

            Dictionary<Rectangle, PdfStream> highlightStreams = page.GetAnnotations()
            .Where(
                (a) => (PdfName.Stamp.Equals(a.GetSubtype()) || PdfName.FreeText.Equals(a.GetSubtype()))
                       && a.GetNormalAppearanceObject().IsStream())
            .ToDictionary(a => a.GetRectangle().ToRectangle(), 
                a => (PdfStream) a.GetNormalAppearanceObject());

        foreach (var pdfAnnotation in page.GetAnnotations())
        {
            page.RemoveAnnotation(pdfAnnotation);
        }