SECTION 3.4
91
File Structure
•
A
cross-reference table
containing information about the indirect objects in the
file
•
A
trailer
giving the location of the cross-reference table and of certain special
objects within the body of the file
This initial structure may be modified by later updates, which append additional
elements to the end of the file; see Section 3.4.5, “Incremental Updates,” for
details.
Header
Body
Cross-reference
table
Trailer
FIGURE 3.2
Initial structure of a PDF file
As a matter of convention, the tokens in a PDF file are arranged into lines; see
(EOL) marker, which may be a carriage return (character code 13), a line feed
(character code 10), or both. PDF files with binary data may have arbitrarily long
lines. However, to increase compatibility with other applications that process
PDF files, lines that are not part of stream object data are limited to no more than
255 characters, with one exception. Beginning with PDF 1.3, the
Contents
string
of a signature dictionary (see Section 8.7, “Digital Signatures”) is not subject to
the restriction on line length. See also implementation note 12 in Appendix H.