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                               APPENDIX E


                E   PDF Name Registry

This appendix discusses a registry, maintained by Adobe for developers, that con-
tains private names and formats used by PDF producers or Acrobat plug-in ex-
tensions.

Acrobat enables third parties to add private data to PDF documents and to add
plug-in extensions that change viewer behavior based on this data. However,
Acrobat users have certain expectations when opening a PDF document, no mat-
ter what plug-ins are available. PDF enforces certain restrictions on private data
in order to meet these expectations.

A PDF producer or Acrobat viewer plug-in extension may define new types of
actions, destinations, annotations, security, and file system handlers. If a user
opens a PDF document and the plug-in that implements the new type of object is
unavailable, the viewer behaves as described in Appendix H, “Compatibility and
Implementation Notes.”

A PDF producer or Acrobat plug-in extension may also add keys to any PDF
object that is implemented as a dictionary, except the file trailer dictionary (see
Section 3.4.4, “File Trailer”). In addition, a PDF producer or Acrobat plug-in may
create tags that indicate the role of marked-content operators (PDF 1.2), as
described in Section 10.5, “Marked Content.”

To avoid conflicts with third-party names and with future versions of PDF, Adobe
maintains a registry for certain private names and formats. Developers must only
add private data that conforms to the registry rules. The registry includes three
classes:

• First class. Names and data formats that are of value to a wide range of de-
  velopers. All names defined in any version of the PDF specification are first-


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