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SECTION 3.4                                                           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
Section 3.1, “Lexical Conventions.” Each line is terminated by an end-of-line
(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.

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