Returns the appearance for mode in the appearance state state, whatever AS says.
public PdfFormXObject? GetAppearance(PdfAppearanceMode mode, CosName state)
Normal, rollover or down.
The appearance state, such as On or Off; ignored when the entry is a single stream.
null when there is none.ISO 32000-2 §12.5.5, Table 170, with the fallbacks of GetAppearance(PdfAppearanceMode).