PATENT CLARIFICATION NOTE

Adobe has a number of patents covering technology that is disclosed
in the Portable Document Format (PDF) Specification, version 1.3 and
later, as documented in PDF Reference and associated Technical Notes
(the Specification). Adobe desires to promote the use of PDF for
information interchange among diverse products and applications.

Accordingly, the following patents are licensed on a royalty-free,
non-exclusive basis for the term of each patent and for the sole
purpose of developing software that produces, consumes, and
interprets PDF files that are compliant with the Specification:

[
  This should not be construed as legal advice!

  Given that all these patents are at least 20 years past the date of
  their issuance, my understanding is that they are now in the public
  domain (i.e., expired). If you wish to do something with them that 
  might possibly be infringing, I would suggest consulting an IPL 
  attorney to confirm this! Note that Adobe still holds various 
  PDF-related trademarks which are protected under IP Law. 

  PDF itself is now under open standard ISO 32000-2
  See https://pdfa.org/pdf-standards/
  Closely related is the archival document standard (PDF/A subset of PDF)
    found in ISO 19005. This concerns avoiding external references and
    encryption, and device-independent color and other specifications.
  There are other PDF variants of lesser concern to us at this time,
    including PDF/X (high quality printing) and 
    PDF/VT (graphics data exchange).
]

U.S. Patent Numbers:

    5,634,064
    5,737,599
    5,781,785
    5,819,301
    6,028,583

In addition, the following patent is licensed on a royalty-free, non-
exclusive basis for its term and for the sole purpose of developing
software that produces PDF files that are compliant with the
Specification (specifically excluding, however, software that
consumes and/or interprets PDF files):

U.S. Patent Number:

    5,860,074

The above licenses are limited to only those rights required to
implement the Specification and no others. That is to say, Adobe
grants only those rights in the above patent(s) necessarily practiced
to implement the Specification, and does not grant any rights not
required to implement the Specification. The licenses do not grant
the right to practice any patent covering other technologies, such as
implementation techniques that are not explicitly disclosed in the
Specification, nor does it allow the use of any patented feature for
any purpose other than as set forth in the applicable license grant.
Adobe has other patents in various fields, none of which are hereby
licensed.
