Sustainability of Digital Formats: Planning for Library of Congress Collections

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PDF/A-1, PDF for Long-term Preservation, Use of PDF 1.4

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name ISO 19005-1. Document management - Electronic document file format for long-term preservation - Part 1: Use of PDF 1.4 (PDF/A)

PDF/A-1 is a constrained form of Adobe PDF version 1.4 intended to be suitable for long-term preservation of page-oriented documents for which PDF is already being used in practice. The ISO standard [ISO 19005-1:2005] was developed by a working group with representatives from government, industry, and academia and active support from Adobe Systems Incorporated.

The PDF/A standards attempt to maximize:

  • Device independence
  • Self-containment
  • Self-documentation

The constraints include:

  • Audio and video content are forbidden
  • Javascript and executable file launches are prohibited
  • All fonts must be embedded and also must be legally embeddable for unlimited, universal rendering
  • Colorspaces specified in a device-independent manner
  • Encryption is disallowed
  • Use of standards-based metadata is mandated

The PDF/A-1 standard defines two levels of conformance: conformance level A satisfies all requirements in the specification; level B is a lower level of conformance, "encompassing the requirements of this part of ISO 19005 regarding the visual appearance of electronic documents, but not their structural or semantic properties."

Production phase A final-state format for delivery to end users and long-term preservation of the document as disseminated to users.
Relationship to other formats
    Subtype of PDF, Portable Document Format
    Subtype of PDF_1_4, PDF Version 1.4
    Subtype of PDF/A, PDF/A, PDF for Long-term Preservation
    Has subtype PDF/A-1a, PDF for Long-term Preservation, Based on PDF 1.4, Level A Conformance
    Has subtype PDF/A-1b, PDF for Long-term Preservation, Based on PDF 1.4, Level B Conformance

Local use Explanation of format description terms

LC experience or existing holdings LC was represented on the working group for the original PDF/A standard and continues to be active in the development of new versions.
LC preference

The Library of Congress expresses preferences for formats for content (primarily in physical form) for its collections through the "Best Edition" specification from the U.S. Copyright Office in Circular 7b. Rev: 08 ⁄ 2010 of Circular 7b lists formats acceptable for mandatory deposit of Electronic Serials available only online, in order of preference. For page-oriented renditions, PDF/A (this version or later versions) appears first on the list. Other forms of PDF are acceptable, preferably with searchable text.

In general, PDF/A is a preferred format for page-oriented textual (or primarily textual) documents when layout and visual characteristics are more significant than logical structure. Note that, for PDFs based on page images digitized by scanning, the source images are considered the master format if available. PDFs created from those images may be optimized for access convenience rather than sustainability.

Sustainability factors Explanation of format description terms

Disclosure Open standard, approved in May 2005 and published by ISO in September 2005. Developed by the working group ISO/TC 171 SC2, Document Imaging Applications, Application Issues, for which AIIM (The Association for Information and Image Management) acts as secretariat. ISO has formed a Joint Working Group, which also includes ISO/TC 46 SC11, Archives/records Management, ISO/TC 130, Graphics Technology, and ISO/TC 42, Photography.
    Documentation ISO 19005-1:2005. Document management -- Electronic document file format for long-term preservation -- Part 1: Use of PDF 1.4 (PDF/A-1). The standard cannot be used without PDF Reference, Third Edition, Version 1.4, which it uses as a normative reference.

Since the standard was published in late 2005, tools for creation, conversion, and validation have been reaching the market steadily. Adobe's own Acrobat Professional 7.0 allowed saving files in a form compliant with the draft standard. Acrobat 8 and later versions support the standard as published. Microsoft Office 2007 supports creation of PDF/A files through Save as PDF, an add-on module. Open Office introduced support for PDF/A in release 2.4 (in early 2008).

Several commercial companies with products aimed at large enterprises, have produced products supporting the creation, migration, and validation of PDF/A files: Apago, Inc., Visioneer (for scanning paper to PDF/A), Callas Software, Compart Systemhaus, Luratech, Nuance, PDF Tools AG. Many of these companies are based in Europe, where the growing requirements from the EU for use of digital formats that are formal (preferably ISO) standards has produced more market pressure than in the U.S. Starting with version 0.93 (released in January 2007), the widely used open source FOP (Formatting Object Processor, based on the W3C's XSL-FO standard) from Apache, has support for the minimal PDF/A profile, PDF/A-1b. Lists of supporting products are found at:

The standards development process involved active participation on behalf of communities whose endorsement or adoption would create significant momentum for wider adoption in the sense of requirement or preference for PDF/A over generic PDF for archival deposit or submission. Important groups are government agencies and legislative and judicial institutions. Adobe reported migration of legacy "report silos" at several (un-named) financial institutions at a meeting of the European DLM (Document Lifecycle Management) Forum in Helsinki in November 2006. An increasing number of libraries and other archival institutions are recommending or requiring PDF/A. For pragmatic reasons, when PDF/A is mandated, PDF/A-1b is usually acceptable. Full PDF/A-1a compliance, with tagged document structure, is hard to achieve except in a workflow that anticipates that objective from initial document creation. A few examples of libraries and archives recommending or mandating PDF/A are: Virginia Tech for electronic theses; National Archives of Norway; University of Texas Libraries for textual documents deposited in a digital repository. The United States Patent and Trademarks Office (USPTO) has requirements for PDFs that it accepts for electronic filing; the requirements are based on the PDF/A specification. Documents conforming to PDF/A-1 meet the USPTO requirements. As of March 2014, PDF/A-1 is a preferred format for textual documents, scanned text, presentations, and posters for transfer of permanent electronic records to the U.S. National Archives.  For scanned text, additional image quality guidance is given.

According to an announcement available on the PACER (Public Access to Court Electronic Records -- for U.S. Federal Courts) web site in February 2011, "The Judiciary is planning to change the technical standard for filing documents in the Case Management and Electronic Case Filing (CM/ECF) system from PDF to PDF/A."

A list of entities recommending or requiring use of PDF/A was found at from Adobe between 2010 and early 2013 (link now via Internet Archive at Another list of entities recommending or requiring use of PDF/A by 2011 is found at from the PDF Association, an alliance of vendors;

    Licensing and patents

Adobe has a number of patents covering technology that is disclosed in the Portable Document Format (PDF) Specification, version 1.3 and later, and hence in the ISO 19005-1 specification by reference. As an ISO standard, the compliance of ISO 19005-1 with the ISO/IEC/ITU common patent policy has been vetted.

A summary of relevant information on the Adobe Web site in September 2010 (see follows.

To promote the use of PDF for information interchange the following patents are licensed by Adobe on a royalty-free, non-exclusive basis for the term of each patent for developing software that produces, consumes, and interprets PDF files : 5,634,064 (filed 1996-08-02, granted 1997-05-27); 5,737,599 (filed 1995-12-07, granted 1998-04-07); 5,781,785 (filed 1995-09-26, granted 1998-07-14); 5,819,301 (filed 1997-09-09, granted 1998-10-06); 6,028,583 (filed 1998-01-16, granted 2002-02-22); 6,289,364 (filed 1997-12-22, granted 2001-09-11); 6,421,460 (filed 1999-05-06, granted 2002-07-16). Patent 5,860,074 (filed 1997-08-14, granted 1999-01-12) is similarly licensed on a royalty-free, non-exclusive basis for its term but only for the purpose of developing software that produces PDF files (thus specifically excluding software that consumes and/or interprets PDF files).

In association with the adoption of PDF, version 1.7 as an ISO standard (ISO 32000-1:2008), Adobe issued a Public Patent License, granting "every individual and organization in the world the royalty-free right, under all Essential Claims that Adobe owns, to make, have made, use, sell, import and distribute Compliant Implementations."

Transparency Depends upon compliant software tools to read. Building tools requires sophistication. PDF/A does not permit encryption.
Self-documentation Support for embedding any form of metadata for a document is extremely good. Use of XMP is mandatory for basic descriptive and identifying metadata. Other XMP metadata packages can be embedded.
External dependencies PDF/A is constrained to avoid external dependencies. All necessary fonts must be embedded.
Technical protection considerations PDF/A does not permit encryption.

Quality and functionality factors Explanation of format description terms

Normal rendering Good support is possible, but not guaranteed. The PDF/A format does not preclude creating documents from scanned page images; such files do not necessarily support indexing of the document text or extraction of text for quotation.
Integrity of document structure The logical structure of a document is only represented in a PDF/A file if the creator or process during creation takes steps to incorporate structural tagging. The PDF/A standard recommends the representation of structural hierarchy.
Integrity of layout and display PDF is designed to represent the layout of page-oriented documents.
Support for mathematics, formulae, etc. Can be represented by embedded graphics.
Functionality beyond normal rendering Annotations may be embedded. Bookmarks may be provided.

File type signifiers and format identifiers Explanation of format description terms

Tag Value Note
Filename extension pdf
The standard does not indicate that a different extension should be used to distinguish PDF from PDF/A.
Indicator for profile, level, version, etc. See note.  The standard specifies that the PDF/A version and conformance level of a file shall be specified using the PDF/A Identification extension schema defined in the standard. This schema has two mandatory elements: pdfaid:part (integer) and pdfaid:conformance (closed list of text values). A PDF-1 file should have the integer value 1 for pdfaid:part.

Notes Explanation of format description terms


Developed to address the issue that large bodies of official documents and important information are maintained in PDF, but that PDF is not suitable as an archival format. The Administrative Office of the U.S. Courts was a driving force in forming a U.S. Committee to initiate an ISO standard based on PDF. The activity has been under the joint auspices of AIIM and NPES (National Printing Equipment Suppliers).

Part 2 of ISO 19005 (as of February 2011, approved as an ISO Final Draft International Standard) extends the capabilities of Part 1, described here. The newer version is based on PDF version 1.7 (as defined in ISO 32000-1) rather than PDF version 1.4.

Format specifications Explanation of format description terms

Useful references


Last Updated: Tuesday, 21-Feb-2017 09:34:59 EST