Gets the font the glyph is shown in: the one Tf (or the Font entry of a graphics state parameter dictionary)
selected; Helvetica's Standard 14 metrics when text is shown before any font is selected or the font is missing.
public PdfFont? Font { get; }
ISO 32000-2 §9.3.1 and §9.5. Glyph selection and Unicode mapping are the font's, on demand.