Sustainability of Digital Formats
Planning for Library of Congress Collections
Sustainability of Digital Formats
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| Introduction | Sustainability Factors | Content Categories | Format Descriptions | Contact | |
| Full name | ISO 19005-2. Document management - Electronic document file format for long-term preservation - Part 2: Use of ISO 32000-1 (PDF 1.7) |
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| Description |
PDF/A-2 is a constrained form of Adobe PDF version 1.7 (as defined in ISO 32000-1) intended to be suitable for long-term preservation of page-oriented documents for which PDF is already being used in practice. See PDF/A for more information about the PDF/A family of standards. See PDF/A-1 for information about the previous version of the standard. The primary difference between PDF/A-1 and PDF/A-2 is the use of a later underlying version of PDF. Added capabilities are through compliance with ISO 32000-1 and include:
The PDF/A-2 standard defines three 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." An intermediate level of conformance has been introduced for PDF/A-2; Level U conformance represents Level B conformance with the additional requirement that all text in the document have Unicode equivalents. The support for JPEG 2000 is restricted in ways that increase compatibility with PDF/X, e.g., constraining the number of color channels (to 1, 3, or 4). |
| 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_7, PDF, Version 1.7 (ISO 32000-1:2008) |
| Subtype of | PDF/A, PDF for Long-term Preservation |
| Has earlier version | PDF/A-1, PDF for Long-term Preservation, Use of PDF 1.4 |
| Has subtype | PDF/A-2a, PDF for Long-term Preservation, Use of ISO 32000-1 (PDF 1.7), Level A Conformance |
| Has subtype | PDF/A-2u, PDF for Long-term Preservation, Use of ISO 32000-1 (PDF 1.7), Level U Conformance |
| Has subtype | PDF/A-2b, PDF for Long-term Preservation, Use of ISO 32000-1 (PDF 1.7), Level B Conformance |
| Has extension | PDF/A-3, PDF for Long-term Preservation, Use of ISO 32000-1, with Embedded Files |
| 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. |
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| 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. Circular 7b (as reviewed in 9/2012) lists formats acceptable for mandatory deposit of Electronic Serials available only online, in order of preference. For page-oriented renditions, PDF/A 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. |
| Disclosure | Open standard, approved in October 2010 and to be published by ISO in 2011. 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. under the auspices of ISO. It is a Joint Working Group, including participation from ISO/TC 46 SC11, Archives/records Management, ISO/TC 130, Graphics Technology, and ISO/TC 42, Photography. |
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| Documentation | ISO 19005-2:2011. Document management -- Electronic document file format for long-term preservation -- Part 1: Use of ISO 32000-1 (PDF/A-2). The standard cannot be used without ISO 32000-1. Document management -- Portable document format -- Part 1: PDF 1.7, which it uses as a normative reference. |
| Adoption |
The compiler of this format description is unable to determine the degree to which different versions and conformance levels of PDF/A are created and used. See PDF/A for a discussion of adoption of PDF/A in general. Comments welcome. |
| Licensing and patents | See PDF/A. |
| Transparency | See PDF/A. |
| Self-documentation | See PDF/A. |
| External dependencies | See PDF/A. |
| Technical protection considerations | See PDF/A. |
| Text | |
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| Normal rendering | See PDF/A. |
| Integrity of document structure | See PDF/A. |
| Integrity of layout and display | See PDF/A. |
| Support for mathematics, formulae, etc. | See PDF/A. |
| Functionality beyond normal rendering | See PDF/A. |
| Tag | Value | Note |
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| Filename extension | pdf |
The standard does not indicate that a different extension should be used to distinguish PDF from PDF/A. |
| Internet Media Type | See related format. | See PDF/A. |
| Magic numbers | See related format. | See 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/A-2 file should have the integer value 2 for pdfaid:part. |
| File signature | See related format. | See PDF/A. |
| General | See PDF/A. |
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| History | See PDF/A. |
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