Question: In which ISO format is print data best archived?
Answer: As PDF/A is rather emphatic and distinctive about assuring long-term reproducibility or reutilization of PDFs, the print data that is sent to the printers as PDF/X must best be created as PDF/A too, so that archiving is possible immediately without additional processing.
Question: I already have printable PDF/X files. Will I face problems when converting to PDF/A?
Answer: No, conversion takes place mostly without problem – basically, every PDF/X-1a or PDF/X-3 file must also be saved simultaneously as PDF/A-1b.
Question: What are the differences between PDF/A and PDF/X?
Answer: The two standards PDF/X and PDF/A were developed by ISO to be largely compatible with each other – i.e. a PDF file can be simultaneously compliant with PDF/A and PDF/X.
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.
Question: Can a PDF/A file be simultaneously compliant with PDF/X and vice-versa?
Answer: Yes, both PDF/X and PDF/A have been intentionally developed by ISO in such a way that a PDF document can conform to both standards at the same time. Thus, although typographical aspects – e.g. information on trappings – are not explicitly demanded by the PDF/A standard, they are not forbidden either. PDF/A also doesn’t forbid creation of PDFs so that they will be considered as production-compatible in the graphics industry. In detail, divergences between PDF/A and PDF/X have indeed resulted from the development chronology of standards. In practice, these minor differences seldom pose a problem and conversions ought to be smooth.
Question: How do you generate a simultaneous PDF/A & PDF/X compliant file?
Answer: With the Preflight functions developed by callas software, like in Adobe Acrobat 8 Professional, a simultaneous PDF/X and PDF/A compliant document can be created from a PDF in a single step – simply set up a Preflight profile where both standards can be activated in the “Convert to PDF/X or PDF/A” menu. You can try out the whole thing using Acrobat Professional 8 – the Preflight functions available there offer various options, e.g. save a PDF/A as PDF/X; or save a PDF as PDF/A and as PDF/X in one go. With the correction options available in Preflight you can also sort out some problems through appropriate correction.
On the contrary, Adobe Acrobat Professional 7 offers PDF/A support only to some extent, as the PDF/A standard was not yet fully ready during the development of Acrobat 7. If automatable solutions are demanded, the pdfInspektor CLI and pdfaPilot CLI from callas software can help: Both command-line modules are based exactly on the same source code as the Preflight function in Acrobat, however run unmanned in Server mode, alternately on Windows, Mac OS X, Linux or Sun. They can be integrated in Helios or Switch environments without any problem.