1. Building the book at the wrong page size.
The selected KDP trim size and the PDF page size must agree. A manuscript created on letter or A4 pages may look like a book, but it is not a book interior until the page size matches the selected product.
This is especially common when authors export from Word, Google Docs, Canva, PowerPoint, or a template that was never built for the final trim.
2. Treating bleed as optional decoration.
Bleed is not a style choice. It is needed when an image, color, rule, or background reaches the edge of the page or cover. If the book needs bleed, the file has to be built with bleed dimensions. If it does not need bleed, adding it can create confusion and unnecessary warnings.
Covers always need to account for bleed. Interiors need it only when interior content reaches the edge.
3. Ignoring the gutter until the proof arrives.
The gutter is the inner margin near the spine. If it is too narrow, the book may be technically approved but physically uncomfortable. Readers should not have to flatten the book to see the inner words.
Longer books need more inside room. A formatting choice that seems efficient on screen can become cramped in print.
4. Reusing a cover after the interior changes.
A full-wrap cover is tied to the final page count and paper choice. Add pages, remove pages, change cream to white, or change ink and the spine calculation can move. The old cover may no longer fit.
Many cover problems are not design problems at all. They are mechanical mismatches between the cover file and the final interior.
5. Putting important content in unsafe zones.
Back cover copy, author photos, logos, prices, spine text, and decorative borders should not crowd trim lines, fold lines, hinge areas, or the barcode zone. A cover can be attractive and still be mechanically wrong.
The same principle applies inside the book. Page numbers and running heads are still live content. They need room.
6. Using low-resolution or stretched images.
Images should be judged at print size, not screen size. A thumbnail, screenshot, compressed social-media image, or small AI output may not hold up across a full page or wraparound cover.
Stretching an image to cover a larger area does not create detail. It creates blur, softness, or artifacts.
7. Exporting through the wrong path.
Every conversion step can change a file. Word to PDF, Canva to PDF, image to PDF, online converter to PDF, and PDF repair tools can each alter fonts, compression, transparency, page boxes, or image quality.
A clean export is deliberate. It preserves page size, embeds fonts, maintains image quality, and produces a PDF that matches the book you actually intend to print.
Need a file checked?
If you have already tried to solve the problem and KDP is still warning or rejecting the file, send the trim size, page count, paper choice, rejected PDF, and the exact warning. We can tell you whether it needs a narrow correction or a deeper rebuild.