Preflight: what to check before you upload
A finished PDF is not the same thing as a printable one. Preflight is the set of checks that sit between those two states, and it takes about fifteen minutes the first time you do it properly.
Do it before you order the proof. A proof of a file with an unembedded font tells you nothing except that the file had an unembedded font.
The list, in the order it matters
1. Page size matches your trim, exactly, on every page. Not "close to." A 6 × 9 book is 6 × 9 on page 1 and on page 312. Mixed page sizes inside one PDF are common when a title page or an image page was made somewhere else and pasted in, and most printers reject on the first one they find.
2. Bleed where art runs off the edge. If an image is meant to reach the paper edge, it has to extend past the trim line — normally ⅛ inch (3 mm) on every side that bleeds. Without it you get a thin white sliver down one edge on some copies and not others, because trimming has a tolerance.
3. Everything important inside the safe area. Text, faces, logos, page numbers. Anything within about ¼ inch of a trimmed edge is at risk of being cut, and on the inside edge it is at risk of disappearing into the binding.
4. Fonts embedded. The one that ruins books. A PDF either carries the font data inside itself or merely references a font by name and expects the machine opening it to have a copy. If the printer's machine does not, it substitutes — and substitution changes metrics, which re-flows lines, which moves your page breaks. That is how a book comes back set in a typeface you have never used.
5. Images at print resolution, in the right color space. 300 DPI at final printed size, not at whatever size the file happens to be. An image that is 300 DPI at 2 inches wide is 100 DPI at 6 inches. Most printers want CMYK for covers; check rather than assume.
6. Interior ink genuinely black-and-white. If you are paying black-and-white rates, every interior page needs to be black ink only. A single "black" heading that is actually a rich CMYK black, or one chart in color, can push the whole book onto color pricing.
7. No stray blank page at the end. Export tools add them. It is also the single easiest way to end up one page over a threshold.
8. Final page count even, where the printer requires it. Most do. A book is printed on sheets, and a sheet has two sides.
9. Page count matches the spine you built the cover around. The interior and the cover are two separate files that have to agree about one number. If the interior grew by eight pages after you made the cover, the cover is now wrong.
10. Barcode area clear. Leave the block your printer specifies free of artwork and text, on the back cover, in the position they publish.
In the tools. The Interior Formatter exports with fonts embedded and the interior ink set for black-and-white printing, keeps the final page count even, and writes a plain-text report beside the file describing exactly what was produced. That count flows to the Cover Maker so the spine matches. Start a book → · about the tools
The printer's own check is not a review
Every major printer runs an automated preflight on upload, and it is genuinely useful. It catches a wrong page size, a missing bleed, an unembedded font, a page count that disagrees with your declared spine.
What it cannot do is tell you the book is right.
An automated check reads structure, not judgment. It does not know your title is off-center, that your chapter openings drop to three different heights, or that the cover art is the wrong genre entirely. It will pass a file that is technically flawless and commercially a mistake.
Treat "accepted" as "the file parses," not as "the book is good."
Two failure modes, and only one of them is loud
Hard rejections are the good kind. Wrong page size, missing bleed, unembedded fonts, a page count outside the printer's range. The upload stops, you get a message naming the problem, you fix it and upload again. Half an hour, no cost.
Silent acceptances are the expensive kind. These pass every automated check and are still wrong:
- Soft images. A 150 DPI photograph is a valid image. It prints mushy.
- A color page you did not intend. One near-black heading in CMYK, one chart, and your black-and-white book is now a color book.
- A spine 2 mm out. The arithmetic can be within whatever tolerance the check allows and still shift the front artwork visibly.
- Type too close to the gutter. Inside the safe area on paper, unreadable once bound.
- A cover exported at the right dimensions but the wrong scale, so everything is proportionally correct and slightly small.
None of these produce an error message. They produce a box of books.
The defense is not a better automated check. It is looking — at the exported file at 100%, and then at the printed proof.
In the tools. The Cover Maker draws live trim, bleed and safe-area guides while you work, keeps the title and author as live vector text rather than flattened pixels, and reserves the barcode area. Previews are free, unlimited and watermarked. Start a book → · about the tools
What to check by eye, after the machine is happy
Open the final PDF yourself and look at:
- The first page and the last page.
- One chapter opening from each third of the book.
- Any page with an image on it.
- The cover at 100%, then zoomed out to thumbnail size.
Four minutes. It catches the things structure checks cannot see.
The rule
Preflight is what you do before the proof, not instead of it.
Preflight makes sure the printer can produce your file. The proof tells you whether you want what it produced. They answer different questions, and skipping either one costs more than doing both.
Make yours
Everything here is built into the tools, and they are free to use: name your book, bring your manuscript or your artwork, and work as long as you like. You only pay when you want the files without the preview watermark.
Next: White or cream paper? · More: Order the proof. Then read it in daylight · Book cover dimensions, start to finish · How to format a book interior · Where to print