Files the press can trust: a print-ready checklist from our prepress desk.

Prepress is the least romantic room in a printing factory and the one that decides whether the romantic rooms go well. Nothing on this list is exotic. It is the same short set of checks we have run on incoming files for years, and the same short set of problems we find. Work through it before you upload, and your book moves straight to proofing; skip it, and the first days of your schedule are spent on email.

Send a PDF the press understands

We prefer PDF/X. It is a constrained flavor of PDF built for printing: fonts must be embedded, color must be defined, and the ambiguities that make ordinary PDFs unpredictable are simply not allowed. If your layout application can export PDF/X-1a or PDF/X-4, use it. And whatever you export, make sure every font is embedded or outlined — a missing font does not fail loudly. It substitutes quietly, and the reflowed line lands in the finished book.

Color: CMYK, and the two blacks

The press prints four inks. A file built in RGB must be converted to CMYK somewhere, and if you leave that conversion to chance, the vivid electric blues and greens of your screen come back muted — RGB describes light, and some of that light has no equivalent in ink. Convert deliberately, in your own studio, where you can see what changes and adjust.

Then there is black, which on press is two different things. Large solid areas — cover backgrounds, full-page panels — want a rich black, something like C40 M30 Y30 K100, which prints deep and even. Small text wants 100K only: one plate, nothing to misregister, crisp at any size. Set small type in rich black and the finest misalignment gives every letter a colored halo. Related is the overprint question: black text should normally overprint the background beneath it, while colored objects knock out. Most layout software does the right thing by default; the errors come from manual overrides, which is why we preflight for them.

One more limit worth knowing: paper can only hold so much ink. Coated stock tolerates a higher total ink coverage than uncoated, which absorbs more and dries slower. If your rich blacks and deep shadows stack all four channels near their maximums, ask us for the limit for your chosen paper before you build the file.

Geometry: bleed, margins, resolution

Every edge that will be trimmed needs 3mm of bleed — image extending past the trim line, so the knife never reveals a white sliver. In the other direction, keep live matter — text, page numbers, anything that must survive — at least 5mm inside the trim. Trimming is mechanical and accurate, but paper is paper, and a caption set 1mm from the edge is gambling. Images should be 300dpi at final printed size; a 300dpi photograph enlarged to double width in layout is a 150dpi photograph, whatever the file properties say.

The spine is not a guess

The most common error on cover files is a spine width taken from a previous book, a competitor's book, or thin air. Spine width is arithmetic: real paper bulk multiplied by real page count, plus the binding allowance. Two papers of identical weight can differ meaningfully in thickness, so the only reliable number comes from the printer who is holding the actual stock. Ask us for the spine width — never guess. We calculate it from the paper on our shelf and send you a cover template with it drawn in.

Then let paper settle the argument

When the file passes, we make a physical proof — three to five days — and this is the step we ask clients not to skip. A screen is backlit; paper is not. A proof shows you the converted blues, the real weight of your blacks, the trim in your hand. It settles, in one courier envelope, arguments that screenshots sustain for weeks. Approve it, and production runs fifteen to twenty-five days with no surprises left in the file — because there is nothing left in the file we have not both already held.