Difference between revisions of "PDF/A in PDS4 - A Primer"

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== PDF/A Overview ==
 
== PDF/A Overview ==
There are so far three iterations of the PDF/A standard: PDF/A-1, PDF/A-2, and PDF/A-3. A document that conforms to one standard will not necessarily conform to the others. PDS4 requires compliance specifically to the first, PDF/A-1<ref>[https://pds.jpl.nasa.gov/policy/format_policies_final.pdf Policy on Formats for PDS4 Data and Documentation]. (2014, June 30). The Planetary Data System. From [https://pds.jpl.nasa.gov/policy/ PDS Policies]</ref>.
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The Portable Document Format (PDF) is a broad, complex file format. The International Organization for Standardization (ISO) has created various PDF subset standards which are specialized for different uses. The PDF/A standard (ISO 19005) is designed for long-term preservation. There are three iterations of the PDF/A standard so far: PDF/A-1, PDF/A-2, and PDF/A-3. Versions of PDF/A retain backward but not forward compatibility (e.g., a document that complies with PDF/A-2 will also conform to PDF/A-3, but not necessarily to PDF/A-1). PDS4 requires compliance specifically to the first version, PDF/A-1.<ref>[https://pds.jpl.nasa.gov/policy/format_policies_final.pdf ''Policy on Formats for PDS4 Data and Documentation'']. (2014, June 30). The Planetary Data System. From [https://pds.jpl.nasa.gov/policy/ PDS Policies]</ref>
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=== PDF/A-1 ===
 
=== PDF/A-1 ===
PDF/A-1 is based on PDF version 1.4, and imposes further restrictions.
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PDF/A-1 (ISO 19005-1) is based on PDF Version 1.4, and imposes further specifications.
 
: PDF/A-1 files '''must''' include:
 
: PDF/A-1 files '''must''' include:
:* Embedded fonts<ref name="FAQ">[http://www.npes.org/pdf/19005-1_FAQ.pdf 19005-1 FAQ]. (2006, July 10). PDF/A Joint Working Group. From [http://www.npes.org/programs/standardsworkroom/toolsbestpractices/pdfa.aspx NPES PDF/A FAQ]</ref>
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:* Embedded fonts <ref name="FAQ">[http://www.npes.org/pdf/19005-1_FAQ.pdf ''19005-1 FAQ'']. (2006, July 10). PDF/A Joint Working Group. From [http://www.npes.org/programs/standardsworkroom/toolsbestpractices/pdfa.aspx NPES PDF/A FAQ]</ref>
:* Device-independent color<ref name="FAQ"/>
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:* Device-independent color <ref name="FAQ"/>
:* XMP metadata<ref name="FAQ"/>
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:* XMP metadata <ref name="FAQ"/>
 
: PDF/A-1 files '''may not''' include:
 
: PDF/A-1 files '''may not''' include:
:* Encryption<ref name="FAQ"/>
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:* Encryption <ref name="FAQ"/>
:* LZW Compression<ref name="FAQ"/>
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:* LZW Compression <ref name="FAQ"/>
:* Embedded files<ref name="FAQ"/>
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:* Embedded files <ref name="FAQ"/>
:* External content references<ref name="FAQ"/>
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:* External content references <ref name="FAQ"/>
:* PDF Transparency<ref name="FAQ"/>
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:* PDF Transparency <ref name="FAQ"/>
:* Multi-media<ref name="FAQ"/>
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:* Multi-media <ref name="FAQ"/>
:* JavaScript<ref name="FAQ"/>
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:* JavaScript <ref name="FAQ"/>
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There are two levels of conformance:
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:; PDF/A-1b — Level B (Basic) Conformance
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:* This is the minimum conformance level required for PDS4.
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:; PDF/A-1a — Level A (Accessible) Conformance
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:* This is the much preferred conformance level for PDS4.
  
; PDF/A-1a
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Note that it's not immediately apparent whether a PDF file conforms to a standard. All PDF documents are defined by the same file format, after all, and thus they all use the <code>.pdf</code> filename extension. A document that is intentionally standard-compliant should, however, have metadata which specifies its standard. A file which claims to conform to PDF/A-1a, for example, will include the following tags in the <code>pdfaid</code> namespace:
Level A Conformance
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{| width=0%
* This is the much preferred conformance level for PDS4.
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|<pre>
; PDF/A-1b
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<pdfaid:part>1</pdfaid:part>
Level B Conformance
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<pdfaid:conformance>A</pdfaid:conformance></pre>
* This is the minimum conformance level required for PDS4.
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|}
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A PDF reader may make note of this designation. Adobe Acrobat, in particular, displays a blue banner which states that the file "claims compliance with the PDF/A standard." Regardless, this claim of compliance must be [[Creating and Validating PDF/A-1 Documents#Validation|validated]]. A non-compliant document may incorrectly have metadata indicating compliance; conversely, compliance metadata may be missing from an otherwise compliant document.
  
 
== See Also ==
 
== See Also ==

Revision as of 19:48, 7 July 2017

PDF/A Overview

The Portable Document Format (PDF) is a broad, complex file format. The International Organization for Standardization (ISO) has created various PDF subset standards which are specialized for different uses. The PDF/A standard (ISO 19005) is designed for long-term preservation. There are three iterations of the PDF/A standard so far: PDF/A-1, PDF/A-2, and PDF/A-3. Versions of PDF/A retain backward but not forward compatibility (e.g., a document that complies with PDF/A-2 will also conform to PDF/A-3, but not necessarily to PDF/A-1). PDS4 requires compliance specifically to the first version, PDF/A-1.[1]

PDF/A-1

PDF/A-1 (ISO 19005-1) is based on PDF Version 1.4, and imposes further specifications.

PDF/A-1 files must include:
  • Embedded fonts [2]
  • Device-independent color [2]
  • XMP metadata [2]
PDF/A-1 files may not include:
  • Encryption [2]
  • LZW Compression [2]
  • Embedded files [2]
  • External content references [2]
  • PDF Transparency [2]
  • Multi-media [2]
  • JavaScript [2]

There are two levels of conformance:

PDF/A-1b — Level B (Basic) Conformance
  • This is the minimum conformance level required for PDS4.
PDF/A-1a — Level A (Accessible) Conformance
  • This is the much preferred conformance level for PDS4.

Note that it's not immediately apparent whether a PDF file conforms to a standard. All PDF documents are defined by the same file format, after all, and thus they all use the .pdf filename extension. A document that is intentionally standard-compliant should, however, have metadata which specifies its standard. A file which claims to conform to PDF/A-1a, for example, will include the following tags in the pdfaid namespace:

<pdfaid:part>1</pdfaid:part>
<pdfaid:conformance>A</pdfaid:conformance>

A PDF reader may make note of this designation. Adobe Acrobat, in particular, displays a blue banner which states that the file "claims compliance with the PDF/A standard." Regardless, this claim of compliance must be validated. A non-compliant document may incorrectly have metadata indicating compliance; conversely, compliance metadata may be missing from an otherwise compliant document.

See Also

External Links

General
Backend

References

  1. Policy on Formats for PDS4 Data and Documentation. (2014, June 30). The Planetary Data System. From PDS Policies
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 19005-1 FAQ. (2006, July 10). PDF/A Joint Working Group. From NPES PDF/A FAQ