SECTION 10.2
843
Metadata
10.2 Metadata
A PDF document may include general information, such as the document’s title,
author, and creation and modification dates. Such global information about the
document (as opposed to its content or structure) is called
metadata
and is in-
tended to assist in cataloguing and searching for documents in external databas-
es. A document’s metadata may also be added or changed by users or plug-in
extensions (see implementation note 160 in Appendix H). Beginning with PDF
1.4, metadata can also be specified for individual components of a document.
Metadata can be stored in a PDF document in either of the following ways:
•
In a
document information dictionary
associated with the document (Section
•
In a
metadata stream (PDF 1.4)
associated with the document or a component
of the document (Section 10.2.2)
10.2.1 Document Information Dictionary
The optional
Info
entry in the trailer of a PDF file (see Section 3.4.4, “File Trailer”)
can hold a
document information dictionary
containing metadata for the docu-
ment; Table 10.2 shows its contents. Any entry whose value is not known should
be omitted from the dictionary rather than included with an empty string as its
value.
Some plug-in extensions may choose to permit searches on the contents of the
document information dictionary. To facilitate browsing and editing, all keys in
the dictionary are fully spelled out, not abbreviated. New keys should be chosen
with care so that they make sense to users.
The value associated with any key not specifically mentioned in Table 10.2 must
be a text string.
Note:
Although consumer applications can store custom metadata in the document
information dictionary, it is inappropriate to store private content or structural in-
formation there. Such information should be stored in the document catalog instead
(see Section 3.6.1, “Document Catalog”).