You have written the book, formatted the interior and built the cover. What is left is the part that feels least like craft and most like an exam: the upload. You sign in to KDP, fill in the details, attach two files, and wait for a machine to tell you whether the thing you made is allowed through. For most first-time authors this is the most anxious afternoon of the whole project — not because the work is unfinished, but because it is unclear what is even being judged.
Here is the reassuring shape of it. Once your files are made, KDP does not assess whether your book is good. It checks whether your files are correct — a small, fixed, mechanical set of things — and then it shows you a preview and trusts you to confirm the rest. Nothing about the process is mysterious once you know what is being looked at, and in what order. This note is the map of the publish phase: the files KDP wants, what it checks the moment you upload, what only you can check, and where each step is covered in its own depth.
The two files, and why they have to agree
A print book on KDP is two separate uploads: the interior (every page inside the cover) and the cover (a single wide wrap — back, spine and front on one canvas). You make them separately, but KDP checks them as a pair, because a cover is calculated from the book it belongs to.
The number that ties them together is the page count. Your final page count sets the spine width, which sets the full-wrap cover size. Change the interior after the cover is built — add a chapter, change the trim — and the two files no longer fit. This is why the order of operations matters more than anything else in the publish phase: lock the interior completely first, then build the cover to fit it. The two halves are covered in full in how to format a book interior for KDP and how to calculate your KDP cover size.
What KDP checks the moment you upload
When you attach your interior file, KDP runs an automatic pass before it will let you continue. It is checking mechanical, file-level things — the same handful every time:
- The file type and size. A print interior is best supplied as a PDF; KDP also accepts some word-processor formats, but a print-ready PDF is the file least likely to shift between your screen and the press. There is an upper size limit, and very large image-heavy books can run into it.
- The page size. Every page has to be the trim size you selected — no stray different-sized pages, no document still set to A4 or US Letter when the book is meant to be 6 × 9 in.
- Embedded fonts. Every font the file uses must be embedded inside it, so the printer is not guessing at a substitute.
- Image resolution. Artwork should be 300 DPI at its printed size; KDP flags interiors whose images fall well below that.
- Margins and bleed. Content has to sit inside KDP's minimum margins, and a full-bleed book has to actually carry bleed past the trim line.
Most upload failures are one of these five, and each produces a fairly terse message. Reading those messages — and knowing which fault each one points to — is a short skill of its own, set out in common KDP upload errors, and how to fix them. The deeper reasoning behind the interior checks is in why KDP rejects a book interior; the cover has its own equivalent in why your KDP cover was rejected.
The previewer is the real gate
The automatic checks catch broken files. The Print Previewer catches everything else — and it is the single most useful tool in the whole upload. It renders your interior and cover exactly as the press will, with the trim line and margins drawn in, and lets you turn every page. This is where you see a chapter starting on the wrong side, a running head printed on a blank page, an image creeping toward the cut, a spine title drifting off the spine.
Do not rush it. The previewer is the last moment a problem costs you nothing to fix. Walk every page, watch the margins, check the spine, and move on only when nothing surprises you. If the previewer flags something it will not let you ignore, that is a hard fault — and almost always one of the file-level checks above.
Metadata is checked too — not just the files
It is easy to think of the upload as a file problem, but KDP also reviews the words around the book: the title and subtitle, the author name, the description, the keywords and categories you choose. These have rules of their own — they must describe the actual book, must not carry promotional claims or contact details, and must match what is printed on the cover. Getting them wrong can hold up a book that is mechanically perfect. The common traps are gathered in KDP metadata mistakes to avoid.
One metadata decision is large enough to deserve its own piece: whether to take KDP's free ISBN or supply your own. It affects how your book is listed and where else you can sell it, and it cannot be changed after publishing — see do you need an ISBN for KDP?
The one check only you can do
When the files pass and the previewer looks right, KDP will offer you a proof copy — a printed-and-bound copy of your actual book, marked "Not for Resale". Order it. A screen previewer cannot show you the weight of the paper, the way the cover finish catches the light, how the spine sits, or whether the type is comfortable to read at arm's length. Authors who skip the proof are the ones who find a problem after the book is on sale. The machine checks the file; the proof is the only check of the book.
The publish phase, in order
Laid out as a sequence, the work after the file is made looks like this:
- Confirm the two files agree — interior locked, cover built to the final page count and trim.
- Upload and read the automatic checks — file type, page size, fonts, resolution, margins.
- Walk the Print Previewer — every page, with the trim and margins drawn.
- Settle the metadata — title, description, keywords, categories, and the ISBN decision.
- Order a proof copy — and read the real book before anyone else can.
Each step rests on the one before it, which is why a rushed upload so often loops back to the start.
Where Folio Format fits
What makes the publish phase fragile is that the files are built in one place and judged in another. Folio Format keeps the interior and the cover as properties of one book — the trim, margins, page count and export settings all come from the same source — so the files that leave your desk are already the size and shape KDP is about to check for. The studio runs its pre-flight on the manuscript, the metadata you type and the export, catching the common faults on your desk rather than in a rejection email — and leaving the upload screen with fewer surprises, and the proof copy to answer the rest.
Last checked 26 May 2026. Always confirm current Amazon KDP and IngramSpark specifications before uploading final files. Folio Format is designed to help users export KDP-ready files and catch common publishing issues before upload; it makes no claim about platform acceptance.