Internet DRAFT - draft-hardy-pdf-mime
draft-hardy-pdf-mime
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
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Internet-Drafts are draft documents valid for a maximum of six months
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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
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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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