# What is PDF/X-1a, and does KDP require it?

Source: https://kdpbook.io/glossary/pdf-x-1a · Updated 2026-09-28

**PDF/X-1a**: A print-ready PDF standard with embedded fonts and flattened transparency. It is KDP's preferred format for print files.

Checked against KDP Help on 2026-09-28.

PDF/X-1a is a print-ready PDF standard in which every font is embedded, transparency is flattened and colors are set up for printing. KDP prefers PDF/X-1a but doesn't require it: other PDFs are accepted, though comments, forms and other non-printing objects may be removed during review. The rest of KDP's file rules apply either way.

Also called: print-ready PDF, PDF/X.

## The numbers

KDP print file rules (interior and cover):

| 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.io: kdpbook exports the interior and the full-wrap cover as print-ready PDFs sized for KDP.