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.

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)

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)

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.

• 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.

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.

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.

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.