4.15
cross reference table data structure that contains the byte offset start for each of the indirect objects within the file

7.5.4     Cross-Reference Table
The cross-reference table contains information that permits random access to indirect objects within the file so that the entire file need not be read to locate any particular object.


7.5.5     File Trailer
The trailer of a PDF file enables a conforming reader to quickly find the cross-reference table and certain
special objects. Conforming readers should read a PDF file from its end. ("should" not "shall")

7.5   File Structure
7.5.1    General
A basic conforming PDF file shall be constructed of following four elements:
• A one-line header identifying the version of the PDF specification to which the file conforms
• A body containing the objects that make up the document contained in the file
• 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

7.5.8   Cross-Reference Streams
7.5.8.1 General
Therefore, with the exception of the startxref address %%EOF segment and comments, a file may be entirely a sequence of objects.

Implementation limits. C.1
When a conforming reader reads a PDF file with a damaged or missing cross-reference table, it may
attempt to rebuild the table by scanning all the objects in the file. However, the generation numbers of
deleted entries are lost if the cross-reference table is missing or severely damaged. To facilitate such
reconstruction, object identifiers, the endobj keyword, and the endstream keyword should appear at the
start of a line. Also, the data within a stream should not contain a line beginning with the word endstream, aside from the required endstream that delimits the end of the stream.