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                                              1074
    APPENDIX G                                                           Example PDF Files



       27 0 obj
          << /Title ( Subsection 1 )
              /Parent 26 0 R
              /Dest [ 3 0 R /XYZ null 670 null ]
          >>
       endobj

       28 0 obj
          << /Title ( Section 3 )
              /Parent 22 0 R
              /Prev 26 0 R
              /Dest [ 7 0 R /XYZ null 500 null ]
          >>
       endobj

       29 0 obj
          << /Title ( Summary )
              /Parent 21 0 R
              /Prev 22 0 R
              /Dest [ 8 0 R /XYZ null 199 null ]
          >>
       endobj


G.6 Updating Example

    This example shows the structure of a PDF file as it is updated several times; it
    illustrates multiple body sections, cross-reference sections, and trailers. In addi-
    tion, it shows that once an object has been assigned an object identifier, it keeps
    that identifier until the object is deleted, even if the object is altered. Finally, the
    example illustrates the reuse of cross-reference entries for objects that have been
    deleted, along with the incrementing of the generation number after an object has
    been deleted.

    The original file is the one shown in Example G.1 on page 1058. The updates are
    divided into four stages, with the file saved after each stage:

    1. Four text annotations are added.
    2. The text of one of the annotations is altered.
    3. Two of the text annotations are deleted.
    4. Three text annotations are added.

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