A CIDFontType0: a CIDFont whose glyphs are CFF glyph descriptions, selected by CID.
public sealed class PdfCidFontType0 : PdfCidFont
ISO 32000-2 §9.7.4.1 and §9.7.4.2 (p.346-347); Adobe Technical Note #5176 §18-19. The metrics are read as for every CIDFont. The
program is a FontFile3 of subtype /CIDFontType0C (a bare CFF program) or /OpenType (a "CFF " table, whose
"cmap" is not used to select glyphs; §9.9, Table 124). Whether the program is CID-keyed is read from its bytes (a Top DICT that
begins with ROS), not from the subtype: a CID-keyed program maps a CID to the glyph whose charset entry is that CID, and draws it
with the Private DICT and FontMatrix of the Font DICT that FDSelect gives the glyph; any other program uses the CID as the glyph
id. A CID the program has no glyph for has "no glyph", and the font shows the glyph of the CMap's notdef mapping, else of CID 0
(§9.7.6.3).
CIDToGIDMap is defined for CIDFontType2 only (Table 115) and is ignored here. A font without a usable embedded program is
drawn with its Substitute; without one it has no glyphs: GetGlyphId(Int32) returns 0.