The Upload Manuscript and Upload Cover buttons on KDP look reassuring. They are not preflight. They are file selectors. The actual preflight runs after submission, returns a yes-or-no the next morning, and the no rarely tells you which line of the file caused it. The cure is to walk a checklist before the click — the same checklist a working publisher would run.
The list below is in roughly the order an author would walk it. Each item links to the deeper note where one exists.
Interior PDF
1. Trim is set on every page
The PDF page size matches the trim — 6 × 9 in, 5.5 × 8.5 in, whichever you chose — not Letter or A4. Trim size guide.
2. Margins meet KDP's minimums
Outer, top and bottom margins are at least 0.25 in (no bleed) or 0.375 in (with bleed). The inner margin (gutter) scales with page count: 0.375 in up to 150 pages, 0.5 in to 300, 0.625 in to 500, 0.75 in to 700, 0.875 in beyond.
3. Bleed is set correctly
If any interior page has artwork running to the edge, the whole interior is set up with 0.125 in of bleed on every outer edge. If the interior is text-only with white margins, no bleed is needed. Don't mix. Bleed walkthrough.
4. Fonts embed in the exported PDF
Open the PDF in Acrobat or any preview tool with a font-list view. Every typeface used in the book appears as "embedded" or "subset embedded". No "missing fonts" lines.
5. Images are at least 300 DPI at printed size
Not 300 DPI at the source size — 300 DPI at the size they print on the page. A 1200 × 1800 px photograph on a 6 × 9 in canvas is 200 DPI and prints visibly soft.
6. Page count is even, and inside the trim's range
Paperbacks are bound in signatures; an odd-numbered PDF gets a blank added at the end. The platform allows from 24 pages minimum to roughly 828 absolute maximum, with lower maxima on larger trims.
7. Front matter and back matter are present and in order
Title page, copyright, dedication, contents, chapters, acknowledgements, about-the-author. Page numbering switches from Roman to Arabic at chapter one. Front and back matter guide.
8. The exported file is a flattened PDF
Not a Word document. Not a Pages file. Not a layered Illustrator PDF. A flattened, single-layer, fonts-embedded PDF, exported with bleed if needed. PDF/X-1a:2001 is the safest export format.
Cover PDF
9. Spine width is computed from the final page count and paper type
Black-and-white on white: page count × 0.002252 in. Cream: × 0.0025. Premium colour: × 0.002347. Don't round to a "clean" number. Spine width walkthrough.
10. Total cover dimensions are correct
Width = (2 × trim_width) + spine_width + 0.25 in (bleed). Height = trim_height + 0.25 in. Cover size walkthrough.
11. Cover is one flat PDF, not three files
Back cover, spine and front cover laid out left to right in a single PDF spread. Not separate JPEGs. Not a PSD.
12. Barcode safe zone is clear
The 2 × 1.2 in rectangle in the bottom-right of the back cover (0.25 in inset from each edge) has no text or important artwork in it. A flat panel of colour is fine; copy is not.
13. Spine text follows the 79-page rule
Books under 79 pages cannot carry spine text. If yours is under, remove the spine title. A wordless spine is acceptable.
14. Cover trim matches interior trim, to the decimal
If the interior PDF page size is 5.5 × 8.5 in, the cover's front-cover area is also 5.5 × 8.5 in. They cannot disagree.
Metadata and listing
15. Book title and subtitle are final
The title on the cover, the title on the title page, the title on the copyright page and the title in the KDP listing all match. Changing one later means the others drift.
16. Author name matches across the book and the listing
If the title page says "E. M. Author" and the listing says "Edward Author", Amazon will treat them as two different authors.
17. ISBN, if used, is consistent
One ISBN per format. The ISBN on the copyright page matches the one in the KDP listing matches the one on the barcode (if you supply your own barcode rather than letting KDP generate it).
18. Description and keywords are written
The blurb on the KDP listing, the keyword phrases, the BISAC categories. These can be edited later, but it's easier to write them once than retrofit at 3 a.m. on launch day.
19. Pricing and royalty plan is chosen
Royalty (60% minus print cost), distribution choice, Expanded Distribution toggle if you want it. Confirm the prices in every market you publish in, not just the home market.
20. Author copy plans are in
You will want a physical proof. Order one before approving the title for sale. The proof reveals print issues that on-screen previews don't.
One last check
21. Re-open both PDFs at full screen
Look at the cover at full size. Read the spine title. Check that the back-cover copy is legible. Look at the interior at 100%, not zoomed out. Read the first chapter opening. Read the last page.
This sounds obvious. Almost everyone skips it. The errors caught at step 21 — a typo on the back cover, a hairline issue in chapter three, a missing scene break — are the ones a reader will see.
Where Folio Format fits
Folio Format runs the technical half of this checklist automatically before any export leaves the studio. Trim is set from the project. Margins are computed from the page count. Spine width updates live. The barcode safe zone is overlaid on the cover. Bleed consistency is checked. The author copy still has to be ordered, the metadata still has to be written, and you still have to read it through at full size — but the file mechanics are no longer the failure point.