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       SECTION 8.6                                                            Interactive Forms



       FDF Trailer

       The trailer of an FDF file enables an application reading the file to find significant
       objects quickly within the body of the file. The last line of the file contains only
       the end-of-file marker, %%EOF. This marker is preceded by the FDF trailer dictio-
       nary, consisting of the keyword trailer followed by a series of one or more key-
       value pairs enclosed in double angle brackets (<< … >>). The only required key is
       Root, whose value is an indirect reference to the file’s catalog dictionary (see Table
       8.91). The trailer may optionally contain additional entries for objects that are
       referenced from within the catalog.

                            TABLE 8.91 Entry in the FDF trailer dictionary
KEY     TYPE            VALUE

Root    dictionary      (Required; must be an indirect reference) The catalog object for this FDF file (see
                        “FDF Catalog,” below).

       Thus, the trailer has the overall structure

          trailer
              << /Root c 0 R
                  key2 value2
                  …
                  keyn valuen
              >>
          %%EOF

       where c is the object number of the file’s catalog dictionary.


       FDF Catalog

       The root node of an FDF file’s object hierarchy is the catalog dictionary, located
       by means of the Root entry in the file’s trailer dictionary (see “FDF Trailer,”
       above). As shown in Table 8.92, the only required entry in the catalog is FDF; its
       value is an FDF dictionary (Table 8.93), which in turn contains references to other
       objects describing the file’s contents. The catalog may also contain an optional
       Version entry identifying the version of the PDF specification to which this FDF
       file conforms.

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