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      CHAPTER 5                                                                       Text



      Most font programs (and related programs, such as CIDFonts and CMaps) con-
      form to external specifications, such as the Adobe Type 1 Font Format. This book
      does not include those specifications. See the Bibliography for more information
      about the specifications mentioned in this chapter.

      The most predictable and dependable results are produced when all font
      programs used to show text are embedded in the PDF file. The following sections
      describe precisely how to do so. If a PDF file refers to font programs that are not
      embedded, the results depend on the availability of fonts in the consumer appli-
      cation’s environment. The following sections specify some conventions for refer-
      ring to external font programs. However, some details of font naming, font
      substitution, and glyph selection are implementation-dependent and may vary
      among different applications and operating system environments.


 5.5 Simple Fonts

      There are several types of simple fonts, all of which have the following properties:

      • Glyphs in the font are selected by single-byte character codes obtained from a
        string that is shown by the text-showing operators. Logically, these codes index
        into a table of 256 glyphs; the mapping from codes to glyphs is called the font’s
        encoding. Each font program has a built-in encoding. Under some circum-
        stances, the encoding can be altered by means described in Section 5.5.5,
        “Character Encoding.”
      • Each glyph has a single set of metrics, including a horizontal displacement or
        width, as described in Section 5.1.3, “Glyph Positioning and Metrics;” that is,
        simple fonts support only horizontal writing mode.
      • Except for Type 0 fonts, Type 3 fonts in non-Tagged PDF documents, and cer-
        tain standard Type 1 fonts, every font dictionary contains a subsidiary dictio-
        nary, the font descriptor, containing font-wide metrics and other attributes of
        the font; see Section 5.7, “Font Descriptors.” Among those attributes is an op-
        tional font file stream containing the font program.


5.5.1 Type 1 Fonts

      A Type 1 font program is a stylized PostScript program that describes glyph
      shapes. It uses a compact encoding for the glyph descriptions, and it includes hint
      information that enables high-quality rendering even at small sizes and low reso-

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