The most common reason KDP rejects your interior PDF is an inside margin (gutter) that’s too narrow — this single issue accounts for roughly 40% of all rejections. The remaining causes, in order of frequency: page size not matching your selected trim, un-embedded fonts, odd page count, content bleeding into the margin zone, low-resolution images (below 300 DPI), unsupported color spaces, and PDF encryption. KDP’s file creation guidelines list the requirements, but the error messages don’t tell you which one failed.
Here’s a systematic walkthrough of every common cause and exactly how to fix each one.
Why KDP doesn’t tell you what’s wrong
KDP’s automated file check tests your PDF against a list of requirements. When something fails, it reports the failure but not the specific cause. With over 4 million titles published on KDP since its launch, this vague error message is one of the platform’s most common pain points. It means you’re left guessing — unless you know what KDP actually checks.
Here’s the complete list, in order of how commonly they cause rejections.
1. Inside margin (gutter) too narrow
This is the #1 cause of rejected PDFs. The inside margin is the space on the spine side of each page. It needs to be wide enough that text doesn’t disappear into the binding. KDP’s margin requirements scale with page count:
KDP’s minimum inside margin depends on your page count:
| Page Count | Minimum Inside Margin |
|---|---|
| 24–150 pages | 0.375” |
| 151–300 pages | 0.5” |
| 301–500 pages | 0.625” |
| 501–700 pages | 0.75” |
| 701–828 pages | 0.875” |
The fix: Check your current inside margin against the table above. Use the page count after formatting (the actual PDF page count), not your Word document page count. Add at least 0.125” above the minimum for safety. For recommended margin values (not just minimums), see our book margins and gutter guide. The KDP Book Calculator shows exact margin requirements for any trim size and page count combination, so you can verify before exporting.
Pro tip: If you’re close to a page count boundary (e.g., 148 pages), adding a blank page or adjusting leading could push you into the next bracket and require a wider gutter. Check your margin after any change that affects page count.
2. Page size doesn’t match trim size
Your PDF pages must be exactly the trim size you selected in KDP. If you chose 5.5” × 8.5” in KDP, every page in your PDF must be 5.5” × 8.5”. Not 8.5” × 11” (letter size). Not 5.5” × 8.51”. KDP supports specific trim sizes ranging from 5”x8” to 8.5”x11”, and even a 0.01” mismatch will trigger a rejection.
How this happens: You formatted in Word or Google Docs using letter-size paper (8.5” × 11”) and exported without changing the page size. Or your PDF export added a slight offset.
The fix: Open your PDF in any PDF reader. Check File → Properties (or Document Properties) and look at the page size. It must match your KDP trim size exactly.
In Word: Change the page size under Layout → Size before exporting to PDF. Don’t rely on the print dialog to scale it.
3. Fonts not embedded
Every font in your PDF must be embedded — meaning the font data is included in the PDF file itself. If KDP can’t find a font, it substitutes, which can destroy your layout.
How to check: Open your PDF in Adobe Acrobat (the free Reader works). Go to File → Properties → Fonts tab. Every font should show “(Embedded)” or “(Embedded Subset)” next to it.
Common causes:
- System fonts that aren’t licensed for embedding
- Web fonts that block embedding
- Word’s “do not embed fonts” setting being checked
- Exporting from a tool that links fonts instead of embedding them
The fix:
- In Word: File → Options → Save → check “Embed fonts in the file” and “Embed all characters”
- In InDesign: When exporting to PDF, ensure the font embedding option is enabled (it is by default)
- If using a formatting tool (Vellum, Atticus, Cambric), embedding is handled automatically — Cambric’s PDF export engine also sets the correct page size for your trim and calculates margins based on your page count, which eliminates the three most common rejection causes in a single step
4. Odd page count
KDP requires an even total page count (minimum 24, maximum 828 for black-and-white interiors, or 550 for color). Books are printed on sheets of paper — each sheet has two sides. An odd page count means the last sheet would only be printed on one side, which isn’t physically possible.
The fix: Add a blank page at the end of your book. Most formatting tools handle this automatically. In Word, add a page break after your last page of content.
5. Content in the margin area
If any text, header, footer, page number, or image extends into the minimum margin zone, KDP will reject the file. This includes:
- Running headers that are too close to the page edge
- Page numbers that sit in the margin
- Body text that’s flush with the minimum margin
- Images or decorative elements that bleed into margins
The fix: Increase your margins to be safely above the minimums. A good rule: never let any content element come within 0.125” of the minimum margin boundary.
6. Low-resolution images
Any image in your interior must be at least 300 DPI (dots per inch) at the size it’s printed. A 1000px-wide image printed at 3.33” wide is exactly 300 DPI. The same image printed at 6.66” wide is only 150 DPI and will be rejected.
The fix: Check the pixel dimensions of your images and calculate the DPI at the size they appear in your layout. If you’re using author photos, maps, or illustrations, make sure you have high-resolution originals.
Formula: DPI = Pixel width ÷ Print width in inches. If the result is below 300, you need a higher-resolution image.
7. Transparency or unsupported color space
Less common, but it happens. KDP’s print process requires:
- Grayscale color space for black-and-white interiors
- CMYK or sRGB for color interiors
- No transparency effects (these can cause rendering issues)
The fix: When exporting your PDF, check the color space setting. For novels and most non-fiction, grayscale is correct. If you have color images, use CMYK for the most accurate color reproduction.
8. PDF encryption or security settings
If your PDF has any security restrictions (password protection, print restrictions, copy restrictions), KDP will reject it. The file needs to be fully accessible for KDP to process it.
The fix: Re-export without any security settings. In most PDF export dialogs, there’s a “Security” or “Permissions” section — leave it all off.
The systematic approach
If you’re stuck in a rejection loop and can’t figure out the cause:
- Check page size first. Open the PDF, verify every page matches your trim size.
- Check inside margins. Measure the gutter margin on a few pages and compare to the table above.
- Check page count. Is it even? Count the actual PDF pages.
- Check fonts. Open in Acrobat Reader, File → Properties → Fonts. Every font should say “Embedded.”
- Check for content in margins. Look at pages where content comes closest to the edge — running headers, page numbers, and any pages with indented elements or images.
Work through this list in order. The first three items account for roughly 80% of all rejections. The outside margin minimum is 0.25” for all page counts, and the top and bottom margins must each be at least 0.25” as well. For a complete pre-upload review, our Formatting Checklist covers all 35 items KDP checks. And if you need to recalculate margins for a different page count, the KDP Book Calculator shows exact margin requirements for any trim size.
Avoiding the cycle entirely
The rejection-fix-upload cycle exists because KDP doesn’t give you pre-flight validation. You only find out something’s wrong after uploading and waiting.
Some formatting tools — including Cambric, Vellum, and Atticus — have built-in validation that checks your file against KDP and IngramSpark requirements before you export. If you’re tired of the fix-upload cycle and weighing whether to invest in software or hire a professional formatter, our book formatting services vs DIY guide can help you decide. If your margins are wrong or your page count is odd, the tool tells you before you generate the PDF, not after KDP rejects it.
If you’re formatting manually in Word or InDesign, consider running your PDF through a pre-flight checker (Adobe Acrobat Pro has one, or use the free KDP print previewer) before uploading.
The bottom line
KDP’s rejection messages are unhelpful by design — the system checks dozens of things and doesn’t report which one failed. But the actual list of requirements is finite and knowable. Work through the checklist above, fix the first issue you find, and re-upload. Most books that get rejected need exactly one fix to pass.
If you’d rather skip the rejection cycle entirely, Cambric’s export engine handles all six of the most common rejection causes automatically — correct page sizing, margin calculations based on page count, font embedding, even page counts, content safety zones, and proper color space. You format your book, export, and upload a PDF that passes on the first try.