SECTION 8.6
713
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
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
Thus, the trailer has the overall structure
trailer
<< /Root
c
0 R
key
2
value
2
…
key
n
value
n
>>
%%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,”
FDF
; its
value is an
FDF dictionary
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.