PDF/X, and what each flavour forbids

PDF/X is a PDF with the dangerous parts removed

An ordinary PDF can contain RGB images, missing fonts, JavaScript, video, layers, comments, form fields and an unstated colour intent. A press cannot do anything sensible with most of that.

PDF/X is a family of ISO standards defining subsets suitable for exchange. Every flavour requires:

• All fonts embedded.
• No JavaScript, no video, no form fields, no encryption.
• A TrimBox or ArtBox defined, so the finished size is unambiguous.
• An output intent: a named characterisation of the intended printing condition, such as FOGRA39 or Japan Color 2001 Coated.

The last one is the point of the standard. A PDF/X file says what printing condition its colours were prepared for. A plain PDF does not, and everything else is guesswork.

The flavours you will meet

PDF/X-1a:2001 and :2003. The conservative one. Everything must be CMYK or spot (no RGB at all) and all transparency is flattened before export. No live transparency, no colour management inside the file beyond the output intent. Still the default request at a large number of shops, because it cannot surprise their RIP.

PDF/X-3:2002/2003. Permits colour-managed data (RGB and Lab with embedded profiles) leaving conversion to the RIP. Transparency still flattened. Used mostly in Europe, and Scribus’s default export target.

PDF/X-4:2010. Permits live transparency and layers, and colour-managed content. The RIP flattens once, at device resolution, with full knowledge. This is the better standard where the shop’s RIP supports it: no atomic regions in your file, no hairline seams, smaller files.

PDF/X-5 and PDF/X-6. X-5 adds external references (a file that points at another file), rarely used in general commercial work. X-6 (2020) is the modern successor built on PDF 2.0. Neither is what a local shop will ask for.

Choosing, in two questions

1. ”Do you want X-1a or X-4?” Ask. If they say X-1a, send X-1a. If they say “either”, send X-4 for anything with transparency and X-1a for flat line work.
2. ”Which output intent?” Their answer names the profile you convert to. If they cannot say, ISO Coated v2 (FOGRA39) for coated European-style work and Japan Color 2001 Coated for a great deal of Asian work are defensible defaults, but the question is better than the default.

Exporting it

• InDesign / Illustrator: File ▸ Export ▸ Adobe PDF (Print), then the [PDF/X-1a:2001] or [PDF/X-4:2008] preset. Marks and Bleeds ▸ Use Document Bleed Settings and Crop Marks with a 3 mm offset. Output ▸ set the destination and the output intent profile.
• CorelDRAW: File ▸ Publish to PDF ▸ Settings ▸ the PDF/X-1a or PDF/X-4 preset; bleed and crop marks on the Prepress tab.
• Scribus: File ▸ Export ▸ Save as PDF. Choose PDF/X-1a, X-3 or X-4 in the General tab’s compatibility dropdown, set bleed on Pre-Press, and set the output intent profile on the Colour tab: Scribus will refuse to export a PDF/X file without one, which is the standard being enforced correctly.
• Affinity Publisher: File ▸ Export ▸ PDF, with the PDF/X presets in the preset list.

Where the shop’s answer comes from

A shop that says “X-1a only” is usually running an older RIP, or has been burned by a transparency job and does not want the argument. Neither is unreasonable. A shop that says “X-4 preferred” has a modern workflow and is telling you they would rather flatten it themselves, correctly, than receive somebody’s pre-flattened approximation.

If you have a choice and the job has soft shadows, transparency or placed PSDs, X-4 is materially better and the file will be smaller. If the job is flat line work with spot colours, the flavour makes almost no difference and X-1a is one less thing to discuss.

Verifying you got what you asked for

Never trust the preset name. Check the file:

pdfinfo job.pdf | grep -i -E 'page size|pdf version'
pdffonts job.pdf

For the X-conformance claim itself, Acrobat Pro’s Preflight has PDF/X profiles, and the free veraPDF validator, though aimed primarily at PDF/A, also validates PDF/X conformance levels. Ghostscript will tell you about structure but not about conformance.

The limitation

A file can be technically valid PDF/X and still be wrong for the job: correct structure, wrong output intent, images at 90 ppi, artwork 4 mm off the trim. Conformance is a floor, not a check on your work. The standard guarantees the press can process the file. Everything about whether the file is right is the next three lessons.