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                                                96
       CHAPTER 3                                                                     Syntax



       are free (objects number 0 and 3). Object number 3 has been deleted, and the
       next object created with that object number is given a generation number of 7.

       Example 3.5

          xref
          0 6
          0000000003   65535   f
          0000000017   00000   n
          0000000081   00000   n
          0000000000   00007   f
          0000000331   00000   n
          0000000409   00000   n

       Example 3.6 shows a cross-reference section with four subsections, containing a
       total of five entries. The first subsection contains one entry, for object number 0,
       which is free. The second subsection contains one entry, for object number 3,
       which is in use. The third subsection contains two entries, for objects number 23
       and 24, both of which are in use. Object number 23 has been reused, as can be
       seen from the fact that it has a generation number of 2. The fourth subsection
       contains one entry, for object number 30, which is in use.

       Example 3.6

          xref
          0 1
          0000000000   65535 f
          3 1
          0000025325   00000 n
          23 2
          0000025518   00002 n
          0000025635   00000 n
          30 1
          0000025777   00000 n

       See Section G.6, “Updating Example,” for a more extensive example of the
       structure of a PDF file that has been updated several times.


3.4.4 File Trailer

       The trailer of a PDF file enables an application reading the file to quickly find the
       cross-reference table and certain special objects. Applications should read a PDF

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