SECTION 3.4
107
File Structure
files that are not hybrid-reference files; see
the keywords
xref
and
trailer
are no longer
used. Therefore, with the exception of the
startxref
address
%%EOF
segment and
comments, a PDF 1.5 file is entirely a sequence of objects.
Note:
The use of object streams and cross-reference streams is permitted in linear-
ized PDF, with minor modifications to the specification (see Section F.2, “Linearized
Cross-Reference Stream Dictionary
Cross-reference streams contain the entries shown in Table 3.15 in addition to
the entries common to all streams (Table 3.4) and trailer dictionaries (Table 3.13).
Since some of the information in the cross-reference stream is needed by the
consumer application to construct the index that allows indirect references to be
resolved, the entries in cross-reference streams are subject to the following
restrictions:
•
The value of all entries shown in Table 3.15 must be direct objects; indirect ref-
erences are not permitted. For arrays (the
Index
and
W
entries), all their ele-
ments must be direct objects as well. If the stream is encoded, the
Filter
and
DecodeParms
entries in Table 3.4 must also be direct objects. Also, see imple-
Note:
Other cross-reference stream entries not listed in Table 3.15 may be indi-
rect; in fact, some (such as
Root
in Table 3.13) are required to be indirect.
•
The cross-reference stream must not be encrypted, nor may any strings appear-
ing in the cross-reference stream dictionary. It must not have a
Filter
entry that
specifies a
Crypt
filter (see 3.3.9, “Crypt Filter”).
TABLE 3.15 Additional entries specific to a cross-reference stream dictionary
KEY
TYPE
DESCRIPTION
Type
name
integer
(Required)
The type of PDF object that this dictionary describes; must be
XRef
for
a cross-reference stream.
(Required)
The number one greater than the highest object number used in this
section or in any section for which this is an update. It is equivalent to the
Size
en-
try in a trailer dictionary.
Size