What is a preflight check?

What a preflight check actually does

A modern preflight engine opens the PDF (or native Illustrator file), parses every page, and runs a rule set against it. The rules cover four broad categories:

• Structure. Does the file have a declared bleed? Is there a dieline on a non-printing layer? Are the trim and bleed boxes set correctly?
• Color. Is the color mode CMYK plus named spots (not RGB)? Are the spot colors correctly named? Is total ink coverage under the substrate's limit? Is anything set to overprint that shouldn't be?
• Imagery. Is every raster image at least 300 DPI at its placed size? Are any images linked but not embedded?
• Type and marks. Are fonts embedded or outlined? Do barcodes have valid check digits and adequate quiet zones? Are registration marks present where the press needs them?

Each finding is either a critical (job will fail on press), a warning (may print, will probably cause issues), or an info advisory (nothing wrong, worth a look).

Why it matters

Print mistakes are expensive because they're discovered late. Catching a missing bleed or misnamed spot color in Illustrator takes sixty seconds. Catching the same mistake at the plate stage means re-plating (a few hundred dollars). Catching it on press means reprinting the whole run. New plates, new substrate, new ink, pressroom time, and a delayed delivery to the customer. A flexible packaging reprint routinely costs $8–15k. A carton reprint can run much higher.

A preflight pass doesn't guarantee a perfect print, press calibration, ink formulation, and substrate all still matter, but it rules out the class of failures that are decidable from the file alone.

Manual vs automated preflight

Until recently, preflight was done by a prepress technician opening the file and working through a mental checklist. Big print shops still have a dedicated prepress department for exactly this reason. The problem: it doesn't scale, it varies by technician, and it happens after the file has been handed off, which means a round-trip if anything's wrong.

Automated preflight tools (Enfocus PitStop, Preflight, Markzware FlightCheck, Esko's prepress suite) apply the same rule set every time, finish in seconds, and can be run by the designer before handoff. The designer fixes issues in their own tool, not after a phone call from the print shop.

What a preflight will not catch

Preflight engines are rule-based. They're excellent at decidable failures, missing bleed, orphan spots, underlinked images, and weak at judgment calls. They won't catch:

• Typos or wrong copy (that's proofreading).
• A photo that's in focus but the wrong photo.
• Brand color drift that's still technically in-spec.
• Whether the design is actually good.

Preflight eliminates the "file won't print" category of problems so you can focus on the "does this design work" category.