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                                              1037
      SECTION F.2                                      Linearized PDF Document Structure



      The order of these objects is essentially arbitrary. However, wherever a resource
      consists of a multiple-level structure, all components of the structure should be
      grouped together. If only the top-level object is referenced from outside the
      group, the entire group can be described by a single entry in the shared object
      hint table. This helps to minimize the size of the shared object hint table and the
      number of individual references from entries in the page offset hint table. (See
      also implementation note 182 in Appendix H.)


F.2.9 Other Objects (Part 9)

      Following the shared objects are any other objects that are part of the document
      but are not required for displaying pages. These objects are divided into function-
      al categories. Objects within each of these categories should be grouped together;
      the relative order of the categories is unimportant.

      • The page tree. This object can be located in this section because the viewer ap-
        plication never needs to consult it. Note that all Resources attributes and other
        inheritable attributes of the page objects must be pushed down and replicated
        in each of the leaf page objects (but they may contain indirect references to
        shared objects).
      • Thumbnail images. These objects should simply be ordered by page number.
        (The thumbnail image for page 0 should be first, even if the first page of the
        document is some page other than 0.) Each thumbnail image consists of one or
        more objects, which may refer to objects in the thumbnail shared objects sec-
        tion (see the next item).
      • Thumbnail shared objects. These are objects that are shared among some or all
        thumbnail images and are not referenced from any other objects.
      • The outline hierarchy, if not located in part 6. The order of objects should be the
        same as the order in which they are displayed by the viewer application. This is
        a preorder traversal of the outline tree, skipping over any subtree that is closed
        (that is, whose parent’s Count value is negative). Following that should be the
        subtrees that were skipped over, in the order in which they would have ap-
        peared if they were all open.
      • Thread information dictionaries, referenced from the I entries of thread dictio-
        naries. Note that the thread dictionaries themselves are located with the docu-
        ment catalog and the bead dictionaries with the individual pages.

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