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4 Subsets of PDF Files

Portable Document Format (PDF) is an open standard for document exchange. The file format created by Adobe Systems in 1993 is used for representing two-dimensional documents in a manner independent of the application software, hardware, and operating system. Generally there are 4 subsets of PDF files: PDF/X, PDF/A, PDF/E, and PDF/UA. And what are the differences?

PDF/X – PDF for Graphic Exchange
PDF/X is an umbrella term for several ISO standards that define a subset of the PDF standard. The purpose of PDF/X is to facilitate graphics exchange, and it therefore has a series of printing related requirements, which do not apply to standard PDF files. For example, in PDF/X-1a all fonts need to be embedded and all images need to be CMYK or spot colors. PDF/X-3 accepts calibrated RGB and CIELAB colors, while retaining most of the other restrictions of PDF/X-1a.

PDF/X files must not only follow certain restrictions, but also contain a special file identification, inside the PDF, which says which PDF/X version they are. This means that a file can only conform to a single specific PDF/X standard, even if all other requirements are met. The printing conditions or output intent need to be specified in the file. This can be specified in the form of standard profiles using codes, like "CGATS TR 001 SWOP".

PDF/A – PDF for Archiving
PDF/A is a file format for the long-term archiving of electronic documents. It is in fact a subset of PDF, obtained by leaving out PDF features not suited to long-term archiving. This is similar to the definition of the PDF/X subset for the printing and graphic arts. In addition, the standard places requirements on software products that read PDF/A files. A "conforming reader" must follow certain rules including following color management guidelines, using embedded fonts for rendering, and making annotation content available to users.

The standard does not define an archiving strategy or the goals of an archiving system. It identifies a "profile" for electronic documents that ensures the documents can be reproduced exactly the same way in years to come. A key element to this reproducibility is the requirement for PDF/A documents to be 100% self-contained. All of the information necessary for displaying the document in the same manner every time is embedded in the file. This includes, but is not limited to, all content (text, raster images and vector graphics), fonts, and color information. A PDF/A document is not permitted to be reliant on information from external sources (e.g. font programs and hyperlinks). Click here to learn more about PDF/A.

PDF/E – PDF for Engineering

PDF/E is a subset of PDF, designed to be an open and neutral exchange format for engineering and technical documentation. The PDF/E standard specifies how PDF should be used for the creation of documents in engineering workflows.

  • Key benefits of PDF/E include:
  • Reduces requirements for expensive & proprietary software
  • Lower storage and exchange costs (vs. paper)
  • Trustworthy exchange across multiple applications and platforms
  • Self-contained
  • Cost-effectve and accurate means of capturing markups
  • Developed and maintained by PDF/E ISO committee

The standard does not define a method for the creation or conversion from paper or electronic documents to the PDF/E format.

PDF/UA – PDF with Accessibility

PDF/UA (PDF/Universal Accessibility) is a Standards Committee formed by AIIM. The mission of PDF/UA is to develop technical and other standards for the authoring, remediation and validation of PDF content to ensure accessibility for people that use assistive technology such as screen readers for users who are blind.