Sustainability of Digital Formats: Planning for Library of Congress Collections

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PDF, Version 1.6

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name PDF (Portable Document Format), version 1.6

PDF (Portable Document Format), developed by Adobe Systems Incorporated, is described by Adobe as a general document representation language. PDF represents formatted, page-oriented documents. These documents may be structured or simple. They may contain text, images, graphics, and other multimedia content, such as video and audio. There is support for annotations, metadata, hypertext links, and bookmarks.

PDF 1.6 introduced the ability to embed 3D data in the U3D format. This version also introduced the ability to embed files within a PDF file, permitting the PDF to act as a container format. PDF 1.6 is the basis for ISO 24517:2008, Document management--Engineering document format using PDF--Part 1: Use of PDF 1.6 (PDF/E-1).

Version 1.6 of the PDF format specification is dated Nov 2004 and associated with Acrobat and Adobe Reader 7.

Production phase In general, a final-state format for delivery to end users.
Relationship to other formats
    Subtype of PDF, Portable Document Format
    Has earlier version PDF_1_5, PDF, Version 1.5
    Has later version PDF_1_7, PDF, Version 1.7 (ISO 32000-1)
    Has subtype PDF/E-1, not described separately on this site at this time.

Local use Explanation of format description terms

LC experience or existing holdings The Library of Congress creates PDFs as service formats for some content it creates or makes available, including for some scanned historical materials, primarily to support convenient downloading and printing. Some of this content is in version PDF 1.6. Examples (as of early 2019) include: a set of scanned pages with photo captions from the Historic American Engineering Record and an item from the Vietnam-Era Prisoner-of-War/Missing-in-Action Database. See also PDF.
LC preference See PDF.

Sustainability factors Explanation of format description terms

Disclosure Fully documented by Adobe Systems Incorporated. A normative reference for ISO 24517:2008, Document management—Engineering document format using PDF—Part 1: Use of PDF 1.6 (PDF/E-1).
    Documentation PDF Reference, Fifth Edition, version 1.6. November 2004. Adobe Systems Incorporated.

The compilers of this resource have not explored the relative use of different chronological versions of PDF and have no information as to the degree to which PDF 1.6 is used. Comments welcome.

    Licensing and patents See PDF.
Transparency See PDF.
Self-documentation Version 1.4 and later of PDF can include XMP metadata packages. XMP is Adobe's framework for including arbitrary blocks of metadata, using a representation in RDF.
External dependencies None.
Technical protection considerations See PDF.

Quality and functionality factors Explanation of format description terms

Normal rendering See PDF.
Integrity of document structure See PDF.
Integrity of layout and display See PDF.
Support for mathematics, formulae, etc. See PDF.
Functionality beyond normal rendering See PDF

File type signifiers and format identifiers Explanation of format description terms

Tag Value Note
Filename extension pdf
See PDF.
Internet Media Type application/pdf
Media type registered with IANA. See also PDF.
Magic numbers Hex: 25 50 44 46 2D 31 2E 36
From PRONOM. However, the magic number value in the header (%PDF-1.6) declaring the PDF version with which the file complies can be overridden elsewhere in the file. See Note below for more detail.
Pronom PUID fmt/20
See for PDF 1.6.
Wikidata Title ID Q26085319
See for PDF 1.6.

Notes Explanation of format description terms


Identification of chronological versions of PDF can be given in two places in a PDF file. All PDF files should have a version identified in the header with the 5 characters %PDF– followed by a version number. For PDF files conforming to ISO 32000-1:2008 or earlier specifications (i.e. prior to ISO 32000-2:2017), the version number has the form 1.N, where N is a digit between 0 and 7. For example, PDF 1.6 is identified by %PDF–1.6. However, beginning with PDF 1.4, a conforming PDF writer may use the Version entry in the document Catalog to override the version specified in the header. The location of the Catalog within the file is indicated in the Root entry of the file trailer/footer. This override feature was introduced to facilitate the incremental updating of a PDF by simply adding to the end of the file. As a result, it is necessary to locate the Catalog within the file to get the correct version number. Unless the PDF is "linearized," in which case the Catalog is up front, this will require reading the trailer and then using the reference there to locate the Catalog, which will typically be compressed. This has practical implications because format identification tools, including DROID, typically look for particular characters at the beginning of a file (i.e., in the header), to permit identification with minimal effort. DROID can look for characters at the end of the file, but is not able to follow an indirect reference or decompress file contents. When the version number is not the same in the header and the Catalog, there is potential for format identification errors.

The JHOVE PDF module does take account of the situation, stating that for PDF 1.0 - 1.6, "The PDF version is determined by the data specified in the PDF header and the Version key of the document catalog dictionary. In the event that these two values do not match, the Version key is taken as the authoritative value."

History PDF 1.6 was released in November 2004 and associated with Acrobat and Adobe Reader 7. PDF 1.7 was released in November 2006 and associated with Acrobat and Adobe Reader 8.

Format specifications Explanation of format description terms

Useful references


Last Updated: 01/09/2019