"Print-ready" is a printer's term with a specific meaning, and it gets applied loosely to any PDF that looks finished. The distinction is worth having, because a file that is genuinely print-ready is a chore to produce and most documents do not need to be one.
The three page sizes in every print job
This is the concept everything else hangs off, and it is the one people meet for the first time when a printer rejects a file.
- Trim is the finished page — what the reader holds. 6×9 inches, A5, whatever you chose.
- Bleed is a margin of extra artwork *outside* the trim, usually 3mm or 0.125in, that gets cut away. It exists because cutting is accurate to about a millimetre, and a background printed exactly to the trim would show a white sliver on the copies that drift.
- Safe area is an inset *inside* the trim, again a few millimetres, where you keep anything that must not be cut — text, page numbers, logos.
So a page whose background runs to the edge is built larger than its finished size and gets trimmed down. A page with white margins needs no bleed at all, because there is nothing at the edge to lose.
Fonts: embedded, every one
A PDF can either carry the shapes of the letters or refer to a font by name and hope. On a press, hope resolves to a substitution — your book set in something the RIP had lying around, with different metrics and therefore different line breaks on every page.
Every serious exporter embeds by default now, but files that have been through an intermediate step — a print-to-PDF driver, an old converter, a design tool exporting "for web" — can still come out referencing. Why it happens and how to check is a five-minute read that has saved people a print run.
You can verify it yourself: in Acrobat, File → Properties → Fonts lists every face with (Embedded) or (Embedded Subset) beside it. Anything without that tag is a font your printer does not have.
Images at print resolution
300 pixels per inch at the size the image prints. A 1,000-pixel screenshot across a six-inch column is 167ppi and will look soft on paper while looking perfect on your monitor, because your monitor is showing it at about a third of the density. The arithmetic is here.
Line art — diagrams, scans of pen drawings — wants more, 600 to 1,200ppi, because the eye is far less forgiving about a soft edge than a soft photograph.
Colour, and when to stop caring
Presses print in CMYK; screens are RGB; the RGB gamut is bigger. So some colours you can see cannot be printed, and a conversion has to choose a substitute.
| Destination | Colour | Worth worrying about? |
|---|---|---|
| Read on a screen | RGB | No |
| Office or home printer | RGB | No — the driver converts |
| Print on demand (KDP, Lulu, Ingram) | RGB accepted, converted for you | Only for a brand colour you care about |
| Offset, short run | CMYK, often PDF/X-1a | Yes — ask the printer for their spec |
| Anything with a spot or Pantone colour | Separate plate | Yes, and it is their conversation |
Two practical notes for the rows that matter. Black text should be 100% K, not a mix of all four inks: a "rich black" body text needs four plates to align perfectly on every letter, and they will not. And a saturated accent colour — electric blue, bright orange — is the one most likely to come back looking dull, so test it before it becomes your brand.
The other checks a printer runs
- Single pages, not spreads. Imposition — arranging pages onto sheets — is their job, and a file of two-up spreads makes it impossible.
- Consistent page size. One landscape page in 300 portrait ones stops the job.
- No hairlines. A rule defined as "thinnest possible" can print as a broken line. Give every rule a real width, 0.25pt or more.
- No transparency surprises. Flatten drop shadows and blend modes, or expect a grey box.
- Total ink limit. Dark areas mixing all four inks past about 300% do not dry properly. Relevant only if you are building dense artwork.
- No security or password. A protected PDF cannot be processed.
What matters for a PDF nobody prints
Most PDFs are read on a laptop and never touch paper: the lead magnet, the course handbook, the sample chapter, the report. For those, the list collapses to four things.
| Check | Screen-only PDF | |
|---|---|---|
| Fonts embedded | Yes — or it renders wrongly elsewhere | Yes |
| Images sharp | Yes, at 2× for high-DPI screens | Yes, 300ppi |
| Margins that read well | Yes | Yes, plus a gutter |
| Page structure — breaks, numbers | Yes | Yes |
| Bleed | No | Only if art runs to the edge |
| CMYK conversion | No | Ask the printer |
| PDF/X compliance | No | For offset, yes |
The top half of that table is the half that decides whether the document looks professional. The bottom half is the half that decides whether it can be manufactured, and it only applies once someone is manufacturing it.
Before you send it
- Open the exported PDF, not the preview, and read every page at 100%.
- Check the fonts panel for anything not marked embedded.
- Check the page count and page size are what the printer's order says.
- Look at the first and last page of every chapter — that is where breaks go wrong.
- If it is going to press, order a proof and read it on paper. Errors hide on screens.
bukpress handles the top half of this list by construction: A4 pages, fonts embedded on every plan, page numbers and margins you set once, and a preview that mirrors the render rather than approximating it. For a print-on-demand paperback you will still want an interior built at that shop's trim size — what KDP asks for is the detail — but for the far more common case of a PDF someone downloads and reads, this is the whole checklist.