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     SECTION F.2                                       Linearized PDF Document Structure



     The first-page trailer must contain valid Size and Root entries, as well as any
     other entries needed to display the document. The Size value must be the com-
     bined number of entries in both the first-page cross-reference table and the main
     cross-reference table.

     The first-page trailer may optionally end with startxref, an integer, and %%EOF,
     just as in an ordinary trailer. This information is ignored.


F.2.4 Document Catalog and Document-Level Objects (Part 4)

     Following the first-page cross-reference table and trailer are the catalog dictio-
     nary and other objects that are required when the document is opened. These
     additional objects (constituting part 4) include the values of the following entries
     if they are present and are indirect objects:

     • The ViewerPreferences entry in the catalog.
     • The PageMode entry in the catalog. Note that if the value of     PageMode is
       UseOutlines, the outline hierarchy is located in part 6; otherwise, the outline
       hierarchy, if any, is located in part 9. See Section F.2.9, “Other Objects (Part 9)”
       for details.
     • The Threads entry in the catalog, along with all thread dictionaries it refers to.
       This does not include the threads’ information dictionaries or the individual
       bead dictionaries belonging to the threads.
     • The OpenAction entry in the catalog.
     • The AcroForm entry in the catalog. Only the top-level interactive form dictio-
       nary is needed, not the objects that it refers to.
     • The Encrypt entry in the first-page trailer dictionary. All values in the encryp-
       tion dictionary must also be located here.

     Objects that are not ordinarily needed when the document is opened should not
     be located here but instead should be at the end of the file; see Section F.2.9, “Oth-
     er Objects (Part 9).” This includes objects such as page tree nodes, the document
     information dictionary, and the definitions for named destinations.

     Note that the objects located here are indexed by the first-page cross-reference
     table, even though they are not logically part of the first page.

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