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      SECTION 5.5                                                           Simple Fonts



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5.5.5 Character Encoding

      A font’s encoding is the association between character codes (obtained from text
      strings that are shown) and glyph descriptions. This section describes the charac-
      ter encoding scheme used with simple PDF fonts. Composite fonts (Type 0) use a
      different character mapping algorithm, as discussed in Section 5.6, “Composite
      Fonts.”

      Except for Type 3 fonts, every font program has a built-in encoding. Under cer-
      tain circumstances, a PDF font dictionary can change a font’s built-in encoding to
      match the requirements of the application generating the text being shown. This
      flexibility in character encoding is valuable for two reasons:

      • It permits showing text that is encoded according to any of the various existing
        conventions. For example, the Microsoft Windows and Apple Mac OS oper-
        ating systems use different standard encodings for Latin text, and many appli-
        cations use their own special-purpose encodings.
      • It permits applications to specify how characters selected from a large character
        set are to be encoded. Some character sets consist of more than 256 characters,
        including ligatures, accented characters, and other symbols required for high-

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