The numbers
| Rule | KDP requirement |
|---|---|
| Preferred standard | PDF/X-1a; other PDF/X and PDF files are accepted |
| Fonts | embedded, preferably fully rather than as subsets |
| Transparency | flattened before export |
| Pages | single pages, not spreads or 2-up |
| Images | at least 300 DPI; up to 600 DPI recommended |
| Smallest text and lines | 7 pt text; 0.75 pt (0.01 in) lines |
| Gray fills | at least 10% |
| Not allowed | crop marks, trim marks, printer's marks, bookmarks, comments, annotations, invisible objects, placeholder text, metadata, locks or encryption |
| File size | up to 650 MB (40 MB or less recommended for the cover) |
What the standard means
PDF/X is a family of ISO standards for exchanging print files. PDF/X-1a is the strictest common flavor: fonts must be embedded, transparency must be flattened, and colors must be defined for print (CMYK or spot colors, no RGB). A file that passes it leaves little to interpretation at the printer.
Drop shadows, soft glows and semi-transparent layers are stored as transparency. Flattening turns them into plain artwork, so they print the way they looked on screen.
How to export one
InDesign, Affinity Publisher and Acrobat Pro have PDF/X-1a export or conversion presets. Microsoft Word and Google Docs can't write PDF/X, but KDP accepts their PDFs as long as the fonts are embedded and the pages are the right size. Either way, check the result in KDP's previewer before you publish.
Example: two ways to a valid file
A picture book laid out in Affinity Publisher at 8.5 × 8.5 in with bleed is exported with the PDF/X-1a preset: fonts embedded, soft shadows flattened, single 8.625 × 8.75 in pages, no crop marks.
A novel written in Word is exported as a regular PDF at 6 × 9 in with fonts embedded. Both are file types KDP takes; the first leaves less to chance when the book has transparency or complex art.
Common mistakes
- Exporting two-page spreads instead of single pages.
- Leaving crop marks or bleed marks on in the export settings.
- Fonts not embedded, often because a font's license forbids embedding.
- Password-protecting or locking the PDF.
- Leaving comments, bookmarks or placeholder text such as "Lorem ipsum" in the file.
In kdpbook: kdpbook exports the interior and the full-wrap cover as print-ready PDFs sized for KDP.