PDF/X-4 explained

PDF/X-4 is the print exchange standard most workflows should be using today. It keeps the guarantees that matter, and drops the restriction that caused the most damage.

The important difference: transparency stays live

Under PDF/X-1a and PDF/X-3, transparency has to be flattened before export. Flattening converts overlapping transparent artwork into a mosaic of opaque shapes that approximates the original. It usually looks right, but it is destructive and it is where the classic problems come from: faint seams across a gradient, hairline joins in a drop shadow, text that has been converted to outlines to survive the process.

PDF/X-4 permits live transparency. The artwork is preserved as authored, and flattening happens at the RIP where it can be done at output resolution with full knowledge of the device. It is the same job done later, better, and only once.

Layers are also permitted, which matters for versioned artwork and for jobs carrying a technical layer such as a cut contour or white underbase.

What it still requires

The parts worth keeping did not change:

• All fonts embedded
• An output intent, stating the printing condition the file was prepared for
• No encryption, no external references
• Colour-managed RGB is allowed alongside CMYK and spot

So you get the same blind-exchange guarantee as X-1a: the printer can output it without asking you anything. You just avoid the destructive step.

When not to use it

When the printer asks for something else. Some RIPs, particularly older ones, either do not handle live transparency or handle it inconsistently, and a shop that has been bitten by that will specify PDF/X-1a deliberately. That is a reasonable position and not one to argue with.

If nobody has specified a standard, PDF/X-4 is the right default.