PDF In-Depth

When can a PDF reader claim conformance with the PDF standard?

November 08, 2010


Editor's Note: Olaf Druemmer is the CEO of callas software. This article originally appeared on druemmer.com, and has been reprinted with permission.

PDF 1.7 has become an ISO standard in 2008 under the auspices of ISO TC 171 SC 2. As a consequence the further development of PDF is not controlled any longer by Adobe but rather by ISO. Unknown to many, ISO is not a standards producing service organisation, but rather a democratically organized international standards body. ISO standards are not produced by ISO, but rather by technical committees coordinated by ISO where each participating country delegates their national experts to do the actual work, and each participating country has one vote when it comes to accepting or rejecting a draft ISO standard. National standards bodies are open to participation from parties affected by such standardization work - usually it is a matter of getting in touch with the national standards body (and in some countries an annual fee is to be paid to fund the standardization work) in order to become involved in national and ISO standardization work.

ISO TC 171 SC 2, now being in charge of the PDF format, is currently working on the next version, most probably to be called PDF 2.0. A number of additions to the PDF syntax are being discussed. One of the relatively new activities consists of work that defines more explicitly what a conforming reader must support under all circumstances, and where a reader may decide not to support a certain aspect of PDF. In ISO language, a "PDF reader" is an application that reads or consumes a PDF, and then offers some kind of access to the PDF and its contents. Thus both an onscreen viewer for PDFs as well as a printer reproducing a PDF on paper are "PDF readers", but also a metadata extraction tool for extracting metadata from a PDF file is a PDF reader.

While working on the definition of what conforming readers are, and when a reader is not to be considered a conforming reader, it turned out there are so many different types of readers that a single definition may not be feasible. Why should a PDF tool that only extracts text from a PDF be bothered with getting the display of page content of the PDF right? As a consequence it is now most likely that the guiding principle in PDF 2.0, when it comes to defining "reader conformance", will be: a reader can freely chose which aspects of the PDF 2.0 standard to implement - but for any aspect that is implemented it must completely follow the rules for that aspect.

Some examples:

  • if a reader offers rendering of page content, such rendering must be done in full conformance with PDF 2.0 provisions about rendering of page content all color spaces, transparency blend modes, optional content and so forth must be supported
  • a reader does not have to offer support for video, Flash or 3D models but if it does offer such features, they must be implemented in a way that fully conforms to PDF 2.0 (otherwise the reader can not be considered a PDF 2.0 conforming reader)

While this sounds easy and straightforward it should not be forgotten that a number of otherwise good quality PDF readers are far even from having implemented all relevant features. A lot of these PDF readers are still catching up with features introduced a number of years back in PDF 1.4 (for example transparency) or PDF 1.5 (for example optional content). Even when it only comes to rendering page content, only products from Adobe or based on Adobe technology seem to achieve a good coverage of all applicable features in the currently most recent version of PDF, i.e. PDF 1.7 as defined in ISO 32000-1.

With the more explicit guidance and rules around reader conformance to be introduced by PDF 2.0 the topic of reader conformance will become more obvious and more important, and in order to be successful in the market of PDF tools and solutions, it might help to be able to claim reader conformance for a given PDF product.

It will still take some time before PDF 2.0 is finalized and published (probably some time in 2012) but now is the time to provide input to the standardization process if needed. Talk to the experts in your national standards organisation. Or get in touch with the PDF/A Competence Center's Technical Working Group - the PDF/A Competence Center has entered into a "Category A" liaison with ISO TC 171 SC 2 and is entitled to provide input to the work on PDF standards, though it does not have any voting rights (this is and will always be a privilege of participating national standards bodies).

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