If you’ve worked with PDF files, you may have heard of PDF/A or PDF/X. But what exactly are these things and how might they be useful to you? In this article we’ll take a quick look at the five standard PDF file specification subsets and what purpose they serve.
PDF files contain descriptions for a wide variety of document primitives such as text, fonts and graphics. However some industries have very specific document requirements for which the standard PDF format is too board. For example, many companies involved in archiving information, require a document format which is completely self contained with no reliance an external entities such as fonts or hyperlinks to websites. As such the ISO has defined a number of tightly controlled PDF specifications which meet the needs of a particular industry by enforcing certain requirements and restrictions.
Each of these specifications (known as a subset) is named “PDF” followed by a “/” character and a letter (or letters) which abbreviate the intended purpose of the subset (ie: PDF/A). Many of the subsets also have multiple versions of their specification which support different requirements since these subsets are constantly evolving (ie: PDF/A-1A and PDF/A-1B). Note though that all PDF files regardless of their specification subset, always have the .pdf filename extension, so you will need to use a tool like Acrobat to determine which specification they fall under.
PDF/E – used in engineering related documentation, this format is designed to handle complex data including 3D, while producing accurate printings of drawings. This format is also based on version 1.6 of the standard PDF file specification. However there appears to be less information currently available on the web about this subset vs other subsets.
PDF/X – facilitates the exchange of graphical information for the purposes of printing. This subset includes requirements for CMYK coloring, embedded fonts, regional definitions for the printable area and bleed. Prohibited items include scripts, interactive fields, audio and video.
PDF/A – used for archiving of information which must be preserved and reproducible without reliance on external resources. PDF/A files therefore contain everything required to open the file (ie: embedded fonts) and forbid dependencies on external resources (ie: hyperlinks). Other restrictions include the prevention of transparency, audio, video, executable scripts, device dependant coloring etc. PDF/A file sizes tend to be larger than standard PDF files because they contain extra resources in order to be self contained. PDF/A files are commonly used in the legal industry as the preferred “archive” format.
PDF/VT – optimized for variable data printing aka “VDP” (the ability to dynamically change content while printing such as when performing a mail merge). PDF/VT files include specially encapsulated entity groups which optimize the processing of both graphics and text. This is useful for companies which require high volume transactional output printing capabilities to produce large numbers of customized prints (ie: billing or marketing materials).
PDF/UA – enables “universal access” by ensuring that the content can be accessed on user assistance devices (ie: devices used by the blind). The main features of PDF/UA files are tags which can be interpreted by special software to provide alternative access to certain parts of the document. For example, tags can indicate that a section should be zoomed in or read to the user through a text audio interpreter.