Whether the font is a composite glyph encoded identity font.
The normal way to identify a character in a font is to use a
standard such as ASCII. Language encodings such as Latin work this way.
For characters outside this range the PDF format allows you to
reference font glyphs directly using the glyph index within the
font. This is known as an identity encoding. Language encodings
such as Unicode work
Identity encodings are very flexible but they do hardwire the
document to a particular font file and as such the font must be
embdded. Care should be taken when operating on identty encoded
embedded font files.