CHAPTER 3
98
Syntax
KEY
TYPE
VALUE
ID
array
(Optional, but strongly recommended; PDF 1.1)
An array of two byte-strings consti-
tuting a file identifier (see Section 10.3, “File Identifiers”) for the file. The two byte-
strings should be direct objects and should be unencrypted. Although this entry is
optional, its absence might prevent the file from functioning in some workflows
that depend on files being uniquely identified.
Note:
XRefStm
, that appears only in the trail-
er of hybrid-reference files, described in “Compatibility with Applications That Do
indicated by the absence of a
Prev
entry in the trailer dictionary).
Example 3.7
trailer
<< /Size 22
/Root 2 0 R
/Info 1 0 R
/ID [ < 81b14aafa313db63dbd6f981e49f94f4 >
< 81b14aafa313db63dbd6f981e49f94f4 >
]
>>
startxref
18799
%%EOF
3.4.5 Incremental Updates
The contents of a PDF file can be updated incrementally without rewriting the
entire file. Changes are appended to the end of the file, leaving its original
contents intact. The main advantage to updating a file in this way (as discussed in
can be saved quickly. There are additional advantages:
•
In some cases, incremental updating is the only way to save changes to a docu-
ment. An accepted practice for minimizing the risk of data loss when saving a
document is to write it to a new file and rename the new file to replace the old
one. However, in certain contexts, such as when editing a document across an
HTTP connection or using OLE embedding (a Windows-specific technology),