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Technical Specifications of PDF/A
PDF/A is based on the PDF 1.4 specification published by Adobe in 2001. The PDF/A standard – formally known as ISO 19005-1:2005, or PDF/A-1 – was approved by the ISO in September 2005. ISO 19005-1 defines “a file format based on PDF, known as PDF/A, which provides a mechanism for representing electronic documents in a manner that preserves their visual appearance over time, independent of the tools and systems used for creating, storing or rending the files.”
PDF/A has been established as a row of standards with several parts. Currently only PDF/A-1 (Part 1) has been approved. PDF/A-1 is further subdivided into two levels of compliance: PDF/A-1a and PDF/A-1b:
PDF/A-1a Level A Conformance
Ensures that the document’s logical structure and semantics, including natural reading order of text is preserved. Additionally, Level A must meet all requirements of Level B.
PDF/A-1b Level B Conformance
Ensures the reproduction of the document without any visual ambiguity, as well as the consistency of colors and rendered text.
PDF/A-1a and PDF/A-1b differ primarily with respect to text extraction. However, this difference should have no impact for scanned documents, provided the files have not been enhanced by means of OCR for searching.
The PDF/A standard is now being refined by the ISO Technical Committee. ISO 19005-1, Part-2 (PDF/A-2) will address some of the new feature added with versions 1.5, 1.6 and 1.7 of the PDF Reference.
