| 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
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.
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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.
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].
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.
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 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:
These parameters also operate on the view of the PDF document when it is opened.
Several subsets of PDF have been published as distinct ISO standards:
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.
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".
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 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.
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:
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.
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 "
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.
| [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. |
This specification replaces RFC 3778, which previously defined the application/pdf Media Type. Differences include: