A PDF is a PDF until it isn't. The file looks identical on screen, opens identically in any viewer, prints fine on a home laser — and then KDP returns it with a message about specifications, or IngramSpark holds it for review, and you discover that "print-ready" is not the same thing as "a PDF". This note is the explanation that ought to come with the term.
What "print-ready" actually means
A print-ready PDF is one a commercial printer can send directly to a press without further preparation. The printer doesn't have to convert it, doesn't have to find missing fonts, doesn't have to guess at the page size, doesn't have to compress the images. The file arrives, it goes through preflight, the answer is "yes", and the next thing that happens is ink on paper.
Five things distinguish a print-ready PDF from an ordinary one.
1. The page size is the exact trim, not "Letter" or "A4"
Open a print-ready PDF and the page dimensions will be the book's finished trim — 6 × 9 in, 5.5 × 8.5 in, whatever you chose — possibly extended by 0.125 in on every outer edge for bleed. They will not be Letter (8.5 × 11 in) or A4 (210 × 297 mm), even if your manuscript started life there.
A PDF exported at Letter size with a 6 × 9 in book inside it is not print-ready. The printer has no reliable way to crop your content out of the surrounding whitespace, and KDP's preflight rejects the file outright. The fix is to set the page size in your layout tool to the trim before exporting, not to crop in PDF after the fact.
2. Fonts are embedded, not referenced
A PDF can either embed the fonts it uses or reference them by name. A referenced font assumes the printer's system has the same font installed; it usually doesn't. The page renders in a substitute typeface — different metrics, different line breaks, often different language coverage — and the printed book bears no resemblance to the screen preview.
Print-ready PDFs embed every font in full or as a subset. Most layout tools embed fonts by default when exporting to PDF/X-1a:2001 or PDF/X-4. Check the export settings before assuming this is on. If the PDF is built from Word or Pages, confirm the "embed fonts" option is ticked.
3. Images are 300 DPI at printed size
A screen image that looks crisp at 96 DPI prints as visibly soft at the same dimensions. Print needs roughly three times the pixel density to read sharp on paper. The working rule across the publishing industry is 300 dots per inch at final printed size.
This is the spec that most often catches indie authors out. A 1200 × 1800 px photograph looks fine on a 6 × 9 in screen preview. At print resolution, it's 200 DPI — visibly soft, sometimes rejected, often printed with disappointing detail. The image should be at least 1800 × 2700 px for a 6 × 9 in placement, with proportionally more for full-bleed pages.
Vector artwork — anything from Illustrator or Inkscape — is resolution-independent and prints crisp at any size. Use vector wherever the artwork allows, and check raster images individually for resolution at their final placement size.
4. The file is flattened
Layered PDFs, files with active form fields, files with editable text, files with unflattened transparencies — these all confuse print preflight. A print-ready PDF has no live layers, no form behaviour, no editable text fields, no transparencies that haven't been baked into the page.
Most layout tools offer a "flatten transparency" option at export time. PDF/X-1a:2001 is the safest export format for KDP-style print work because it explicitly disallows the features that cause preflight issues. PDF/X-4 is more permissive but supports transparency natively, and KDP currently accepts both.
5. There is bleed where bleed is needed
If your book has any artwork meant to run to the edge of the page, the PDF must extend that artwork 0.125 in (3.175 mm) past the trim line. The printer's blade has a small tolerance; without bleed, the print arrives with thin white edges where the cut overshot.
If your book is text-only with white margins, bleed isn't required. The PDF size matches the trim exactly. This is the cleaner default for novels, most non-fiction and poetry. See the bleed walkthrough for the full mechanism.
The smaller checks that still matter
Beyond the five above, a handful of secondary checks separate "submitted" from "accepted":
- Single PDF, not multiple files. KDP wants one PDF for the interior and one for the cover. Not three. Not a zip.
- RGB or CMYK depending on the platform. KDP currently accepts both. IngramSpark prefers CMYK for colour interiors. Convert before exporting; don't rely on the platform to convert for you.
- No password protection, no print restrictions. The platform's preflight needs to open the file freely.
- Page count is even-numbered for paperbacks. Books are bound in signatures; an odd page count is rounded up by adding a blank.
- File size under the platform's ceiling. KDP allows up to 650 MB for paperback interiors. Most novels run 1–10 MB; photo books and cookbooks can approach the ceiling.
Why this exists
Print-ready PDFs are not arbitrary. Each rule maps to a physical step in the production chain — a guillotine blade's tolerance, an imagesetter's resolution requirement, a printer's RIP software refusing to load a font it can't find. The format was standardised in the early 2000s precisely because publishers were tired of receiving "PDFs" that broke in production.
For indie authors, "print-ready" is the dialect of PDF that says: this file has been prepared for a printer, not for a screen. The tools that build it should know the difference. The author shouldn't have to learn every rule by being rejected.
Where Folio Format fits
Folio Format exports a print-ready PDF as the default for its KDP and IngramSpark paperback and hardback presets. Trim is set from the project. Bleed is set from the interior decision. Fonts embed automatically. Images are flagged at export time if any are below 300 DPI at their placement size. The file that leaves the studio is the file the printer expects.