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Versions: 00 01 02 03 04 05 RFC 8118

Network Working Group                                           M. Hardy
Internet-Draft                                               L. Masinter
Obsoletes: 3778 (if approved)                                D. Markovic
Intended status: Informational                Adobe Systems Incorporated
Expires: August 27, 2017                                      D. Johnson
                                                         PDF Association
                                                               M. Bailey
                                                         Global Graphics
                                                       February 23, 2017


                     The application/pdf Media Type
                        draft-hardy-pdf-mime-05

Abstract

   The Portable Document Format (PDF) is an ISO standard (ISO
   32000-1:2008) defining a final-form document representation language
   in use for document exchange, including on the Internet, since 1993.
   This document provides an overview of the PDF format and updates the
   media type registration of "application/pdf".  It obsoletes RFC 3778.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 27, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  History . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Fragment Identifiers  . . . . . . . . . . . . . . . . . . . .   3
   4.  Subset Standards  . . . . . . . . . . . . . . . . . . . . . .   5
   5.  PDF Versions  . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  PDF Implementations . . . . . . . . . . . . . . . . . . . . .   6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Appendix A.  Changes since RFC 3778 . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   This document is intended to provide updated information on the
   registration of the MIME Media Type "application/pdf" for documents
   defined in the PDF [ISOPDF], "Portable Document Format", syntax.  It
   obsoletes [RFC3778].

   PDF was originally envisioned as a way to reliably communicate and
   view printed information electronically across a wide variety of
   machine configurations, operating systems, and communication
   networks.

   PDF is used to represent "final form" formatted documents.  PDF pages
   may include text, images, graphics and multimedia content such as
   video and audio.  PDF is also capable of containing auxiliary
   structures including annotations, bookmarks, file attachments,
   hyperlinks, logical structure and metadata.  These features are
   useful for navigation, building collections of related documents and
   for reviewing and commenting on documents.  A rich JavaScript model
   has been defined for interacting with PDF documents.

   PDF used the imaging model of the PostScript [PS] page description
   language to render complex text, images, and graphics in a device and
   resolution-independent manner.





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   PDF supports encryption and digital signatures.  The encryption
   capability is combined with access control information to facilitate
   management of the functionality available to the recipient.  PDF
   supports the inclusion of document and object-level metadata through
   the eXtensible Metadata Platform[XMP].

2.  History

   PDF is used widely in the Internet community.  The first version of
   PDF, 1.0, was published in 1993 by Adobe Systems Incorporated.  Since
   then PDF has grown to be a widely-used format for capturing and
   exchanging formatted documents electronically across the Web, via
   e-mail and virtually every other document exchange mechanism.  In
   2008, PDF 1.7 was published as an ISO standard [ISOPDF], ISO
   32000-1:2008.  It was adopted using ISO Fast-Track process and is
   technically identical to Adobe Portable Document Format version 1.7
   [AdobePDF] referenced by [RFC3778].

   The ISO TC-171 committee is presently working on a refresh of PDF,
   known as ISO 32000-2, with a version of PDF 2.0, expected to be
   published in 2017.

   In addition to ISO 32000-1:2008 and 32000-2, several subset standards
   have been defined to address specific use cases and standardized by
   the ISO.  These standards include PDF for Archival (PDF/A) [ISOPDFA],
   PDF for Engineering (PDF/E) [ISOPDFE], PDF for Universal
   Accessibility (PDF/UA) [ISOPDFUA], PDF for Variable Data and
   Transactional Printing (PDF/VT) [ISOPDFVT], and PDF for Prepress
   Digital Data Exchange (PDF/X) [ISOPDFX].  The subset standards are
   fully compliant PDF files capable of being displayed in a general PDF
   viewer.

3.  Fragment Identifiers

   Fragment identifiers appear at the end of a URI, and provide a way to
   reference an anchor to subordinate content within the target of the
   URI, or additional parameters to the process of opening the
   identified content.  The syntax and semantics of fragment identifiers
   is referenced in the media type definition.

   The specification of fragment identifiers for PDF appeared originally
   in [RFC3778], but now will be included in ISO 32000-2 [ISOPDF2].
   This section is a summary of that material.  Any disagreements
   between that document and this should be resolved in favor of the ISO
   32000-2 definition, once that has been approved.

   A fragment identifier for PDF has one or more parameters, separated
   by the ampersand (&) or pound (#) character.  Each parameter consists



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   of the parameter name, "=" (equal), and the parameter value; lists of
   values are comma-separated, and parameter value strings may be URI-
   encoded ([RFC3986]).  Parameters are processed left to right.

   Coordinate values (such as <left>, <right>, <width>) are expressed in
   the default user space coordinate system of the document: 1/72 of an
   inch measured down and to the right from the upper-left corner of the
   (current) page.  ([ISOPDF2] 8.3.2.3 "User Space")

   The following parameters identify subordinate content of a PDF file,
   but also may be used to set the document view to make the (start of)
   the identified content visible:

   page=<pageNum>
      Identifies a specified (physical) page; the first page in the
      document has a pageNum value of 1.

   nameddest=<name>
      Identifies a named destination ([ISOPDF2] 12.3.2.4 "Named
      destinations").

   structelem=<structID>
      structID is a byte string with URI encoding; identifies the
      structure element with ID key within a StructElem dictionary of
      the document.

   comment=<commentID>
      The commentID is the value of an annotation name, which is defined
      by the NM key in the corresponding annotation dictionary (of the
      selected page.  ([ISOPDF2] 12.5.2 "Annotation dictionaries")

   ef=<name>
      Identifies the embedded file where the parameter string <name>
      matches a file specification dictionary in the EmbeddedFiles name
      tree.  If the "ef" parameter is not at the end of the fragment
      identifier, then the rest of the fragment identifier (after the
      ampersand or hash delimiter) is applied to the embedded file
      according to its own media type.  This allows identification of
      content within the embedded file (which itself might be a PDF
      file).

      NOTE: When opening a PDF file that is not from a trusted source,
      processor may choose to prompt the user or even prevent opening of
      the file.

   These parameters also operate on the view of the PDF document when it
   is opened.




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   zoom=<scale>,<left>,<top>
      <scale> is the percentage to which the document should be zoomed,
      where a value of 100 correspond to a zoom of 100%.  <left> and
      <top> are optional, but both must be specified if either is
      included.

   view=<keyword>,<position>
      The arguments correspond to those found in [ISOPDF2] 12.3.2.2
      "Explicit destinations".  keyword is one of the keywords defined
      in [ISOPDF2] "Table 149: Destination syntax" with appropriate
      position values.

   viewrect=<left>,<top>,<width>,<height>
      Set the view rectangle.

   highlight=<left>,<right>,<top>,<bottom>
      Highlight the specified rectangle.

   search=<wordList>
      Open the document and search for one or more words, selecting the
      first matching word in the document. wordList is a string enclosed
      in quotation marks where individual words are separated by the
      space character (or %20).

   fdf=<URI>
      Imports data into PDF form fields.  The URI is either a relative
      or absolute URI to an FDF or XFDF file.  The fdf parameter should
      be specified as the last parameter to a given URI.

4.  Subset Standards

   Several subsets of PDF have been published as distinct ISO standards:

   o  PDF/X, initially released in 2001 as PDF/X-1a [ISOPDFX], specifies
      how to use PDF for graphics exchange, with the aim to fascilitate
      correct and predictable printing by print service providers.  The
      standard has gone through multiple revisions over the years and
      has several published parts, the most recently released being part
      8, specifying different levels of conformance: PDF/X-1a:2001, PDF/
      X-3:2002, PDF/X-1a:2003, PDF/X-3:2003, PDF/X-4, PDF/X-4p, PDF/
      X-5g, PDF/X-5pg and PDF/X-5n.

   o  PDF/A, initially released in 2005, specifies how to use PDF for
      long-term preservation (archiving) of electronic documents.  It
      prohibits PDF features which are not well suited to long term
      archiving of documents, including JavaScript or executable file
      launches.  Its requirements for PDF/A viewers include color
      management guidelines and support for embedded fonts.  There are



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      three parts of this standard and a total of eight conformance
      levels: PDF/A-1a, PDF/A-1b, PDF/A-2a, PDF/A-2b, PDF/A-2u, PDF/
      A-3a, PDF/A-3b and PDF/A-3u.

   o  PDF/E, initially released in 2008 as PDF/E-1 [ISOPDFE], specifies
      how to use PDF in engineering workflows, such as manufacturing,
      construction and geospatial analysis.  Future revisions of PDF/E
      are supposed to include support for 3D PDF workflows.

   o  PDF/VT, initially released in 2010, specifies how to use PDF in
      variable and transactional printing.  It is based on PDF/X, and
      adds adidtional restrictions on PDF content elements and
      supporting metadata.  It specifies three conformance levels: PDF/
      VT-1, PDF/VT-2 and PDF/VT-2s [ISOPDFVT].

   o  PDF/UA, initially released in 2012 as PDF/UA-1 [ISOPDFUA],
      specifies how to create accessible electonic documents.  It
      requires use of ISO 32000's Tagged PDF feature, and adds many
      requirements regarding semantic correctness in applying logical
      structures to content in PDF documents.

   All of these subset standards use "application/pdf" media type.  The
   subset standards are generally not exclusive, so it is possible to
   construct a PDF file which conforms to, for example, both PDF/A-2b
   and PDF/X-4 subset standards.

   PDF documents claiming conformance to one or more of the subset
   standards use XMP metadata to identify levels of conformance.  PDF
   processors should examine document metadata streams for such subset
   standards identifiers and, if apropriate, label documents as such
   when presenting them to the user.

5.  PDF Versions

   PDF format has gone through several revisions, primarily for the
   addition of features.  PDF features have generally been added in a
   way that older viewers "fail gracefully", because they can just
   ignore features they do not recognize.  Even so, the older the PDF
   version produced, the more legacy viewers will support that version,
   but the fewer features will be enabled.  See [ISOPDF] Annex I, "PDF
   Versions and Compatibility".

6.  PDF Implementations

   PDF files are experienced through a reader or viewer of PDF files.
   For most of the common platforms in use (iOS, OS X, Windows, Android,
   ChromeOS, Kindle) and for most browsers (Edge, Safari, Chrome,
   Firefox), PDF viewing is built-in.  In addition, there are many PDF



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   viewers available for download and install.  The PDF specification
   was published and freely available since the format was introduced in
   1993, so hundreds of companies and organizations make tools for PDF
   creation, viewing, and manipulation.

7.  Security Considerations

   PDF is certainly a complex media type as per Section 4.6 of
   [RFC6838], which sets requirements for security analysis of media
   type registrations.  [RFC3778] (which this document obsoletes)
   contained a detailed analysis of some of the security issues for PDF
   implementations known at the time.  While the analysis isn't
   necessarily wrong, the threat analysis is much too limited, and the
   mitigations somewhat out of date.  There is now extensive literature
   on security threats involving PDF implementations and how to avoid
   them, consistent with broad implementation over decades.  We are not
   registering a new media type but rather making a primarily
   administrative update.  With those caveats:

   The PDF file format allows several constructs which may compromise
   security if handled inadequately by PDF processors.  For example:

   o  PDF may contain scripts to customize the displaying and processing
      of PDF files.  These scripts are expressed in a version of
      JavaScript and are intended for execution by the PDF processor.

   o  PDF file may refer to other PDF files for portions of content.
      PDF processors are expected to find these external files and load
      them in order to display the document.

   o  PDF may act as a container for various files embedded in it (for
      example, as attached files).  PDF processors may offer
      functionality to open and display such files or store them on the
      system, such as with the "ef" open action.  THe PDF specification
      places no restrictions on types of files which may be embedded, so
      PDF processors should be extremely careful to prevent unwanted
      execution of attached executables or decompression of attached
      archives which may store dangerous files in the host file system.

   o  PDF files may contain links to content on the internet.  PDF
      processors may offer functionality to show such content upon
      following the link.

   o  The fragment identifier syntax (Section 3) contains directives for
      opening ("ef") or inluding ("fdf") additional material.






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   PDF interpreters executing any scripts or programs related to these
   constructs must be extremely careful to insure that untrusted
   software is executed in a protected environment.

   In addition, the PDF processor itself, as well as its plugins,
   scripts etc. may be a source of insecurity, by either obvious or
   subtle means.

8.  IANA Considerations

   This document updates the registration of "application/pdf", a media
   type registration as defined in [RFC6838]:

   Type name: application

   Subtype name: pdf

   Required parameters: none

   Optional parameter: none

   Encoding considerations: binary

   Security considerations: See Section 7 of this document.

   Interoperability considerations: See Section 5 of this document.

   Published specification: ISO 32000-1:2008 (PDF 1.7) [ISOPDF].  ISO
   32000-2 (PDF 2.0) [ISOPDF2] is currently under development.

   Applications which use this media type: See Section 6 of this
   document.

   Fragment identifier considerations: See Section 3 of this document.

   Additional information:

   Deprecated alias names for this type: none

   Magic number(s): All PDF files start with the characters '%PDF-'
   followed by the PDF version number, e.g., "%PDF-1.7".  These
   characters are in US-ASCII encoding.

   File extension(s): .pdf

   Macintosh file type code(s): "PDF "





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   Person & email address to contact for further information: Duff
   Johnson <duff@duff-johnson.com>, Peter Wyatt
   <Peter.wyatt@cisra.canon.com.au>, ISO 32000 Project Leaders

   Intended usage: COMMON

   Restrictions on usage: none

   Author: Authors of this document

   Change controller: ISO; in particular, ISO 32000 is by ISO/TC 171/SC
   02/WG 08, "PDF specification".  Duff Johnson <duff@duff-johnson.com>
   and Peter Wyatt <Peter.wyatt@cisra.canon.com.au are current ISO 32000
   Project Leaders.

9.  References

9.1.  Normative References

   [ISOPDF]   ISO, "Document management -- Portable document format --
              Part 1: PDF 1.7", ISO 32000-1:2008, 2008.

              Also available free from Adobe.

   [ISOPDF2]  ISO, "Document management -- Portable document format --
              Part 2: PDF 2.0", ISO 32000-2.

              Currently under development - publication expected in
              2017.  This becomes a Normative Reference on approval.

9.2.  Informative References

   [ISOPDFX]  ISO, "Graphic technology -- Prepress digital data exchange
              using PDF -- Part 8: Partial exchange of printing data
              using PDF 1.6 (PDF/X-5)", ISO 15930-8:2008, 2008.

   [ISOPDFA]  ISO, "Document management -- Electronic document file
              format for long-term preservation -- Part 3: Use of ISO
              32000-1 with support for embedded files (PDF/A-3)",
              ISO 19005-3:2012, 2012.

   [ISOPDFE]  ISO, "Document management -- Engineering document format
              using PDF -- Part 1: Use of PDF 1.6 (PDF/E-1)",
              ISO 24517-1:2008, 2008.







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   [ISOPDFVT]
              ISO, "Graphic technology -- Variable data exchange -- Part
              2: Using PDF/X-4 and PDF/X-5 (PDF/VT-1 and PDF/VT-2)",
              ISO 16612-2:2010, 2010.

   [ISOPDFUA]
              ISO, "Document management applications -- Electronic
              document file format enhancement for accessibility -- Part
              1: Use of ISO 32000-1 (PDF/UA-1)", ISO 14289-1:2014, 2014.

   [XMP]      ISO, "Extensible metadata platform (XMP) specification --
              Part 1: Data model, serialization and core properties",
              ISO 16684-1, 2012.

              Not available for free, but there are a number of
              descriptive resources, e.g.,
              <http://en.wikipedia.org/wiki/
              Extensible_Metadata_Platform>

   [PS]       Adobe Systems Incorporated, "PostScript Language
              Reference, third edition", 1999.

   [AdobePDF]
              Adobe Systems Incorporated, "PDF Reference, sixth
              edition", 2006.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, January 2013,
              <http://www.rfc-editor.org/info/rfc6838>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.

   [RFC3778]  Taft, E., Pravetz, J., Zilles, S., and L. Masinter, "The
              application/pdf Media Type", RFC 3778,
              DOI 10.17487/RFC3778, May 2004,
              <http://www.rfc-editor.org/info/rfc3778>.

Appendix A.  Changes since RFC 3778

   This specification replaces RFC 3778, which previously defined the
   "application/pdf" Media Type.  Differences include:






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   o  To reflect the transition from a proprietary specification by
      Adobe to an open ISO Standard, the Change Controller has changed
      from Adobe to ISO, and references updated.

   o  The overview of PDF capabilitiies, the history of PDF, and the
      descriptions of PDF subsets were updated to reflect more recent
      relevant history.

   o  The section on Fragment identifiers was updated to closely reflect
      the material which has been added to ISO-32000-2.

   o  The status of popular PDF implementations was updated.

   o  The Security Considerations were updated to match the current
      understanding of PDF vulnerabilities.

   o  The registration template was updated to match RFC 6838.

Authors' Addresses

   Matthew Hardy
   Adobe Systems Incorporated
   345 Park Ave
   San Jose, CA  95110
   USA

   Email: mahardy@adobe.com


   Larry Masinter
   Adobe Systems Incorporated
   345 Park Ave
   San Jose, CA  95110
   USA

   Email: masinter@adobe.com
   URI:   http://larry.masinter.net


   Dejan Markovic
   Adobe Systems Incorporated
   345 Park Ave
   San Jose, CA  95110
   USA

   Email: dmarkovi@adobe.com





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   Duff Johnson
   PDF Association
   Neue Kantstrasse 14
   Berlin  14057
   Germany

   Email: duff.johnson@pdfa.org


   Martin Bailey
   Global Graphics
   2030 Cambourne Business Park
   Cambridge  CB23 6DW
   UK

   Email: martin.bailey@globalgraphics.com
   URI:   http://www.globalgraphics.com


































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