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An overview of the most important differences between PDF/A and PDF/X

The ISO standards PDF/A (ISO 19005) and PDF/X (ISO 15930) were developed for different purposes. However, many of the requirements of the two standards are exactly the same. The sections below explain the main differences between PDF/A and PDF/X.

Basic differences between PDF/A and PDF/X for printing

PDF/A does not require – but does not forbid – the following technical print-related aspects that are required by PDF/X or are at least more common in PDF/X.

These aspects are required by the PDF/X standard but optional in PDF/A:

  • Page geometry specifications, in particular for TrimBox (specification of the trimmed end format of pages)
  • Trapped setting (specification on whether or not the PDF has already been trapped)

Content that is forbidden in PDF/X but permitted in PDF/A

PDF/X-1a and PDF/X-3 forbid certain elements that are allowed in PDF/A:

  • Comments and form fields in page areas that are to be printed
  • JBIG2 (compression procedure for bitmap image data)

Different metadata requirements

PDF/A has more advanced requirements for metadata than PDF/X-1a and PDF/X-3:

  • If certain metadata is contained in the document information, that metadata must also be contained in the XMP metadata in its equivalent form.

Differences in font handling

  • PDF/X requires the general embedding of fonts, even for invisible text.
  • PDF/A does not require fonts that are used only for invisible text to be embedded.

Invisible text is often used for scanned pages to give a scanned page image text that can be used for OCR text recognition.

Output intent differences

Important: There are separate output intents for PDF/X and PDF/A!

An output intent specifies the output purpose for a PDF file. Examples: A specific printing process such as sheet-fed offset on coated paper, printing on a specific type of digital printer, or output on the screen.

  • PDF/X always requires an output intent.
  • For PDF/X, the output intent must refer to the intended printing method. An output intent for the screen – for example, via sRGB, is not allowed.
  • However, for PDF/A, the output intent is optional – it is only required if device-dependent process color spaces (for example, DeviceCMYK or DeviceRGB) are used in the PDF/A document. If this is the case, the output intent serves to describe the color characterization of the device-dependent color specification
  • With PDF/A, if there are two (or more) output intents, their target profiles must be identical.

Possible problems when converting PDF/X to PDF/A

If a PDF/X file needs to be converted to PDF/A for archiving purposes without losing its PDF/X properties, this can be made particularly difficult if:

  • An output intent without a target profile is used (this is normally permitted for PDF/X-1a and PDF/X-3 as long as there are no device-independent process colors)
  • The file contains comments or form fields (only permitted in PDF/X outside TrimBox/BleedBox) that do not meet the requirements of PDF/A

In most cases, the use of suitable tools such as pdfaPilot or Preflight in Acrobat Professional 8 should make it possible to save a PDF/X file as a PDF/A file without problems occurring.

Possible problems when converting PDF/A to PDF/X

If a PDF/X file needs to be generated from a PDF/A file without the PDF/A properties being lost, this can be made particularly difficult if:

  • The file contains a screen output intent
  • The file contains comments or form fields
  • Scanned pages contain invisible OCR text and the fonts for that text are not embedded

In particular, problems can occur when attempting to store PDF/A documents that were not initially created for production printing as PDF/X files.