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CHAPTER 8                                                         Interactive Features




                                        Header




                                         Body




                                    Cross-reference
                                    table (optional)


                                        Trailer




                           FIGURE 8.10 FDF file structure


FDF Header

The first line of an FDF file is a header, originally intended to identify the version
of the PDF specification to which the file conforms. However, for historical rea-
sons, this version number is now frozen and must read
   %FDF−1 . 2

The true version number is now given by the Version entry in the FDF catalog
dictionary (see “FDF Catalog,” below; see also implementation note 127 in Ap-
pendix H).

FDF Body

The body of an FDF file consists of a sequence of indirect objects representing the
file’s catalog (see “FDF Catalog” on page 713) together with any additional objects
that the catalog may reference. The objects are of the same basic types described
in Section 3.2, “Objects.” Just as in PDF, objects in FDF can be direct or indirect.

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