Both Hidden and Visible fields always show as Default
if (field.Flags == Aspose.Pdf.InteractiveFeatures.Annotations.AnnotationFlags.Hidden)
This condition never is never true even is the field is Hidden when you check the PDF.
I have attached the PDF I'm using to test with. It has several "Hidden" fields but they all show up as Default - even when I try the myForm.GetFieldAppearance("Principal_Name_1") method.