Returns the appearance for mode and the current appearance state (AppearanceState).
public PdfFormXObject? GetAppearance(PdfAppearanceMode mode)
Normal, rollover or down.
null when the annotation has no appearance, or when the entry is a state subdictionary
and AS is absent (a diagnostic: Table 166 requires it) or names a state the subdictionary lacks (legal: nothing is shown).
ISO 32000-2 §12.5.5, Table 170. A missing rollover or down entry falls back to the normal one; a rollover or down state subdictionary that lacks the state falls back to the normal appearance of that state.