A plain PDF with fonts embedded and a total file size under 650 MB is what KDP's paperback submission guidelines specify for an interior file. Those guidelines don't reference a PDF/X standard for interiors at all — PDF/X-1a shows up in cover-file workflows some designers use out of habit, not as a KDP interior requirement.
What KDP's guidelines actually specify
| Requirement | What it says |
|---|---|
| File type | PDF (required if the manuscript has bleeding images or elements); non-bleed manuscripts can also be submitted as DOC, DOCX, RTF, HTML, or TXT and are converted to PDF automatically |
| Fonts | All fonts in the interior file should be embedded before upload |
| File size | Not more than 650 MB total |
| PDF/X | Not mentioned in the paperback submission guidelines |
A coloring book interior is effectively all images, so in practice it's built and exported as a PDF regardless of which non-image formats the guidelines technically allow for text-only manuscripts.
Why PDF/X comes up anyway
PDF/X is a family of ISO standards built for the print and prepress industry, mainly to guarantee that a file's color space, fonts, and bleed marks are unambiguous when it moves between different software and printers. Because it's the safe default in a lot of professional print workflows, some authors and designers assume any print-on-demand platform requires it. KDP's own guidance doesn't ask for it on the interior; asking for PDF/X where it isn't required just adds an export step that changes nothing about whether the file passes KDP's actual checks.
What actually matters for a coloring book PDF
The real requirements for a coloring book interior sit in image and page-formatting guidance, not a PDF-standard checkbox: 300 DPI at the trim's pixel size, 1-bit line art with no gray edge pixels, the interior page count inside KDP's range, the gutter matching that page count, and safe margins respected on every page — the same six checks covered in the interior PDF checklist guide. A file that's technically PDF/X-compliant but fails any of those still fails KDP's review; a plain PDF that clears all of them passes.
Fonts are the one thing worth double-checking
Font embedding is the part of "plain PDF" that's easy to miss on a coloring-book interior, especially one that adds a title or caption line under each drawing. KDP's guidelines call for fonts to be embedded in the native program before export, both for the interior and for cover files. A PDF that references a system font instead of embedding it can render correctly on the machine that built it and still show missing or substituted characters once it's processed elsewhere — checking that fonts are embedded (most export dialogs have an explicit option) avoids that class of problem entirely.
Where the file size limit fits
The 650 MB cap applies to the whole uploaded file, not per page or per image — see the file size limits guide for what that means at typical coloring-book resolutions. A 1-bit, correctly exported coloring book interior sits nowhere near that limit at any coloring-book page count KDP allows; it becomes relevant mainly if pages were accidentally left in a heavier color mode or at an unnecessarily high resolution.
What CrayonMill exports
CrayonMill's export step produces a plain, print-ready PDF — 1-bit line art, no embedded fonts to manage because the interior carries no text, and a file size well under KDP's limit at any book length its 24–300 interior-page range covers. There's no PDF/X option to choose because KDP's guidelines don't call for one on the interior.
Sources
Last verified 2026-09-04. Updated 2026-09-04.