PDF

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File Format
Name PDF
Ontology
Extension(s) .pdf
MIME Type(s) application/pdf
LoCFDD fdd000030, others
PRONOM fmt/276, others
Wikidata ID Q42332

Portable Document Format (PDF) is a document file format originally from Adobe, based on PostScript. It has many subsets.

As well as the 'full function' ISO 32000-1:2008 (or PDF 1.7), there are also PDF/X, PDF/A, PDF/E, PDF/VT and PDF/UA, all of which are ISO specifications.

PDF profiles (formalized subsets) include the following:

  • PDF/A (optimized for preservation)
    • PDF/A-1 (ISO 19005-1:2005)
    • PDF/A-2 (ISO 19005-2:2011)
    • PDF/A-3 (ISO 19005-3:2012) (extends PDF/A-2 by allowing embedded files of any type)
    • PDF/A-4 (ISO 19005-4:2020)
  • PDF/E (ISO 24517-1:2008) (for engineering workflows)
  • PDF/UA (ISO 14289-1) (making documents accessible through assistive technologies)
  • PDF/VT (ISO 16612-2) (support for variable document printing)
  • PDF/X (support for prepress graphics exchange)
    • PDF/X-1 (ISO 15930-1:2001)
    • PDF/X-1a (ISO 15930-4:2003)
    • PDF/X-2 (ISO 15930-5:2003)
    • PDF/X-3 (ISO 15930-6:2003)
  • Tagged PDF

Some scanner documentation references an apparently fictitious "PDF/L" profile (see Gary McGath's "PDF/L?").

A PDF 2.0 spec (ISO 32000-2) was published in 2017-07, with some new features as well as clarification of conformance with existing features.

A PDF/raster draft spec was issued in 2017 as a subset of PDF files containing raster images of scanned documents.

Contents

Identifiers

Format PRONOM LoCFDD
PDF fdd000030
PDF 1.0 fmt/14 fdd000316
PDF 1.1 fmt/15
PDF 1.2 fmt/16
PDF 1.3 fmt/17
PDF 1.4 fmt/18 fdd000122
PDF 1.5 fmt/19 fdd000123
PDF 1.6 fmt/20 fdd000276
PDF 1.7 fmt/276 fdd000277
PDF 1.7, Ext. 3 fdd000313
PDF 2.0 fmt/1129
PDF/A fdd000318
PDF/A-1 fdd000125
PDF/A-1a fmt/95 fdd000251
PDF/A-1b fmt/354 fdd000252
PDF/A-2 fdd000319
PDF/A-2a fmt/476 fdd000320
PDF/A-2b fmt/477 fdd000322
PDF/A-2u fmt/478 fdd000321
PDF/A-3a fmt/479 fdd000360
PDF/A-3b fmt/480
PDF/A-3u fmt/481
PDF/A-4 fdd000532
PDF/X-1 fmt/144, fmt/145 fdd000124
PDF/X-1a fmt/157, fmt/146
PDF/X-2 fmt/147
PDF/X-3 fmt/158, fmt/148
PDF/X-4 fmt/488
PDF/X-4p fmt/489
PDF/X-5g fmt/490
PDF/X-5pg fmt/491
PDF/X-5n fmt/492
PDF/UA-1 fdd000350
PDF/E-1 fmt/493
PDF, Geospatial fdd000315
GeoPDF 2.2 fdd000312

Identification

The majority of PDF files can be identified by a fixed header e.g. "%PDF-1.4", however, older documents have a number of variations.

Compression

Images in PDF documents may use the following compression schemes:

Digital Rights Management & Encryption

PDF has two types of 'encryption' - it uses an 'user' password to limit the ability to open the document, and a 'creator' password to limit other rights, like printing, copying, etc. The former case, where a password is required to open the file, is the main preservation concern, as our users will not be able to open a PDF encrypted in this way (unless the password can be cracked, which may be problematic both technically and legally). However, the latter case causes problems, because the PDF is encrypted here too, but with a special known user password of "" (an empty string, which is not the same as no password). So, the document is encrypted in both cases, and you can only tell which is which by attempting to decrypt the PDF using the special default password "". Some PDF analysis tools (notably JHOVE) do not implement the relevant decryption workflow, and so cannot distinguish between the two types of encryption.

An example of the decryption test workflow can be found here: https://gist.github.com/anjackson/5237071

Some of the most locked-up PDFs anywhere can be found at the ANSI IBR Standards Portal, which has made certain standards documents that are incorporated into legislation available for browsing, but only through a convoluted procedure involving downloading a special plug-in and filling out a registration form that must be re-filled-out in every browsing session.

A "Protected PDF" (PPDF) format is reportedly used by Microsoft's Azure Rights Management Service for sharing files securely within a workgroup.

Document redaction

Occasionally the attempts of technically-inept users to obscure content in PDF files get in the news. People have sometimes had the mistaken impression that if a section of text is overlayed with a solid-black shape, or set to white-on-white text, or some such thing, before the publicly distributed document is sent out, that would make the redacted sections unavailable; this is not true, as it is in fact easy to find text that has been obscured in such manners, often as simple as dragging a mouse over it to highlight it. This happened in a 2018 Florida case connected with the school shooting there, where some parts of the school district's report about the shooter were badly redacted and disclosed by a local newspaper, leading to a judge threatening punishment of the paper and prior restraint of future publications of theirs because of this "hacking", raising all sorts of legal and constitutional issues.

Web linking

When linked on the Web, specific pages of a PDF can be referenced by appending #page=N (where N is the desired page number) as a fragment identifier at the end of the URL. This is a little-known fact.

Specifications

Software

Online utilities

Sample files

See also

Links

Format info

Validation

Jailbreaking

Commentary

Miscellaneous

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