PDF/A facts – an introduction to the standard

PDF/A in a Nutshell 2.0 – PDF for long-term archiving

Current file formats used by popular applications are simply not suitable for public authorities, businesses and individual users needing to store unalterable digital documents for long periods of time. Word processors such as Microsoft Word or OpenOffice Writer create files which can look very different depending on the platform used to view them. Text and images may appear different than intended – or they may not appear at all. Nowadays, there are also the questions of how these programs will develop in the future, and whether or not it will still be possible to open and view older files – an unacceptable risk when considering the timescales involved in long-term archiving.

PDF/A is an industry-recognised ISO standard. Future software development must reflect the need to work reliably with these documents.

An archiving format

When using email or the internet to distribute carefully designed documents containing text and images, users are increasingly choosing PDF. After all, the Portable Document Format can embed all elements of a document within itself. This can include fonts and images, but also 3D objects, audio and video. Embedded fonts are optional; it is also possible (in order to save on file size, for example) to link to one instead. This, however, carries the risk that not all machines will correctly display the PDF.

PDF has also gained such broad worldwide acceptance because free programs exist for all devices and operating systems to view PDF documents. Whether viewed on a tablet, a smartphone or a desktop computer, a PDF file will usually look the same.

Document archives, however, require an exceptionally high standard: the content must always appear exactly the same under all circumstances. Particularly because of its universal availability and worldwide acceptance, it makes sense to build on PDF to create an archiving standard for digital documents.

Why PDF/A and not just PDF?

Put in the simplest possible terms, PDF/A is a PDF which forbids certain functions which could hinder long-term archiving. PDF/A also demands that the file meet certain requirements which guarantee reliable reproduction.

For example, files must not be encrypted with a password, as all content must always be fully available. Embedded video and audio data are also prohibited: PDF/A consciously avoids anything that requires external software for display or playback. JavaScript and certain actions are also forbidden, as executing them could potentially alter the PDF.

PDF/A also places higher demands on the information it contains. All required fonts (or at least all glyphs for the specific characters used) must be embedded within the PDF. To ensure a uniform colour appearance on a variety of platforms and devices, colour information must be given in a platform-independent format using ICC colour profiles. The software must also use the XMP format for metadata (which is used to store the data identifying the file as a PDF/A, for example).

PDF/A also sets technical limits: for example, the page size is limited to an edge length of either 5.08 metres (PDF/A-1) or up to 381 kilometres (PDF/A-2 and PDF/A-3).

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About Alexandra Oettler

Alexandra Oettler ist (Co-) Autorin der Bücher PDF/A kompakt und PDF/A kompakt 2.0.

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