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                                             48
    CHAPTER 3                                                                    Syntax



      represent the document structure and are described separately. Section 3.7,
      “Content Streams and Resources,” discusses PDF content streams and their as-
      sociated resources.



                                 Objects

                                    File           Content
                                 structure         stream

                                Document
                                 structure




                                FIGURE 3.1 PDF components


    In addition, this chapter describes some data structures, built from basic objects,
    that are so widely used that they can almost be considered basic object types in
    their own right. These objects are covered in Sections 3.8, “Common Data
    Structures”; 3.9, “Functions”; and 3.10, “File Specifications.”

    PDF’s object and file syntax is also used as the basis for other file formats. These
    include the Forms Data Format (FDF), described in Section 8.6.6, “Forms Data
    Format,” and the Portable Job Ticket Format (PJTF), described in Adobe
    Technical Note #5620, Portable Job Ticket Format.


3.1 Lexical Conventions

    At the most fundamental level, a PDF file is a sequence of 8-bit bytes. These bytes
    can be grouped into tokens according to the syntax rules described below. One or
    more tokens are assembled to form higher-level syntactic entities, principally
    objects, which are the basic data values from which a PDF document is
    constructed.

    PDF can be entirely represented using byte values corresponding to the visible
    printable subset of the ASCII character set, plus white space characters such as
    space, tab, carriage return, and line feed characters. ASCII is the American
    Standard Code for Information Interchange, a widely used convention for

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