Almost every first-upload problem comes from not separating those two. People build one file, upload it to both, and get a preview full of warnings for reasons that are obvious once the distinction is clear: a fixed page cannot reflow, and a reflowable file has no pages to print.
The Kindle ebook
KDP accepts several formats for the ebook, and they are not equivalent in outcome.
| Upload | Result | Verdict |
|---|---|---|
| EPUB | Converted to Amazon's own format, structure intact | What to send |
| .docx | Converted, with whatever Word's structure implies | Works; less predictable |
| A print PDF | Fixed pages, no reflow, no type-size control | Do not |
| KPF from Kindle Create | Amazon's own tool, Amazon's own file | Fine if you like the tool |
The third row is the mistake worth naming. A PDF uploaded as an ebook produces a book the reader cannot resize the type in, which is the one thing e-reader owners expect. It is technically accepted and it earns bad reviews.
Everything you upload is converted on Amazon's side, so what survives is structure rather than layout: headings, paragraphs, emphasis, lists, tables, images, the table of contents built from your headings. What EPUB carries and what it does not is the fuller version.
The ebook checklist
- A navigable table of contents, generated from real headings rather than typed by hand with page numbers. Page numbers mean nothing in a reflowable file.
- Each chapter starting on its own — a heading break, not a run of empty paragraphs.
- No page numbers, headers or footers. There are no pages.
- A cover image of roughly 1,600 × 2,560 pixels, a 1:1.6 ratio, as JPEG or TIFF. The longest side should be at least 1,000 pixels or it will look poor in the store.
- Front matter kept short. The reader's sample is the opening percentage of the file, and six pages of praise quotes spend it before the book starts.
The paperback interior
This is a print job, and the requirements are the ones any printer has. A PDF, built at the finished page size, with fonts embedded and margins that account for the binding.
Trim size first. Everything else depends on it. KDP offers a list — 5×8, 5.25×8, 5.5×8.5 and 6×9 inches are the common ones for text-led books, with 6×9 the default for nonfiction and trade paperback fiction. Your PDF pages must be that size. A4 is not on the list.
Then margins. The outside margins have a minimum, and the inside margin — the gutter — grows with page count, because a thicker book loses more of the inner edge into the spine. KDP publishes this as a table; the shape of it is:
| Page count | Minimum gutter | Outside margins |
|---|---|---|
| 24–150 | 0.375 in | 0.25 in minimum, 0.5 in comfortable |
| 151–300 | 0.5 in | As above |
| 301–500 | 0.625 in | As above |
| 501–700 | 0.75 in | As above |
| 701–828 | 0.875 in | As above |
Minimums are minimums. A book set to the minimum outside margin looks cramped and reads worse — margins are larger than you think is the design argument, and it applies here with a hard floor underneath it.
The rest of the interior
- Embedded fonts. Every face, fully embedded. A PDF that references a font it does not carry is the classic rejection, and why it happens is worth understanding once.
- Single pages, not spreads. Upload page 1, page 2, page 3 — never two-up.
- Bleed only if you need it. Ink running to the edge means building the page 0.125 in larger on the bleeding edges. A text-only interior does not need bleed and is simpler without it.
- 300ppi images. The arithmetic and the reason low-resolution art gets flagged in the preview.
- A copyright page with the year, your name and the ISBN if you are using your own.
The paperback cover
Not the same file as the ebook cover, and not three files. It is one PDF covering back, spine and front as a single spread, with bleed on all four sides.
The spine width comes from your page count multiplied by the thickness of a sheet of the paper you chose — roughly 0.0023 inches a page for white paper, slightly more for cream. So the cover cannot be finished until the interior is, because adding four pages changes the spine and shifts everything on it.
The rejections people actually hit
- "Content outside the printable area." Something is inside the margin — usually a page number placed too near the trim, or a wide table.
- "Fonts not embedded." Exported by something that assumed the reader has the font.
- Low-resolution images. A 72ppi screenshot at full width.
- Trim size mismatch. The PDF is A4 or Letter while the listing says 6×9.
- Wrong spine width. The cover was built before the final page count.
- A PDF uploaded as the ebook. Accepted, then reviewed badly by readers who cannot change the type size.
Every one of these is caught by KDP's own previewer before publication. Run it, page through the whole book rather than the first spread, and order a proof copy for anything you care about. A proof is a few pounds and shows you things no screen does — the proof pass is part of the pipeline for a reason.
Where bukpress fits, stated plainly
For the Kindle ebook, this is a direct fit: write in Markdown, design once, and export the EPUB with your headings as the book's structure, your typefaces packaged in, and your artwork as the native cover. That is the file KDP wants.
For a paperback interior, it is not. bukpress exports A4, and a KDP paperback needs pages built at a trim size on Amazon's list. If print is the destination, that part of the job belongs somewhere that sets an arbitrary page size — which is the honest version of this rather than a hedge.
For everything that is a PDF people read on a screen — the lead magnet, the course workbook, the sample chapter, the review copy — A4 is exactly right, and that is most of what most authors actually send.