Free KDP Interior PDF Checker

The rejection nobody sees coming

Most interiors that come back rejected come back for the same reason: the inside margin. It is the one against the spine, and the requirement is not fixed. A thick book does not open flat, so the more pages you have the more room the binding swallows, and the minimum steps up as the book gets longer. A layout that passed at 140 pages fails at 160 without a word of the text changing.

That is a horrible thing to discover after a proof copy has been printed and posted to you. It is trivial to discover here, because the page count and the margin are both sitting in the file already.

What it measures, and how

Page count and trim size come from the page box, so they are exact, and the trim is checked against the list of standard sizes. That catches the common accident of a manuscript left at A4 or US Letter, which prints at a size no reader wants to hold. It also checks that every page is the same size, because a single stray page at a different size is rejected outright.

The margins are measured from the text itself. Every glyph run on every page carries a position and a font, so the ink boundary of each page can be worked out precisely, and the tightest margin found anywhere in the book is the one reported, because that is the one a printer cares about. The inside and outside margins are tracked separately and swap sides on alternate pages, the way a bound book actually works.

Artwork is checked by comparing each image's real pixel size against the size it is drawn at on the page, which gives its effective resolution. Anything under 300 dpi is flagged with the page it is on. A picture can be enormous and still print badly if it has been scaled up, and this is the number that tells you.

What it cannot tell you

Whether your fonts are embedded. That is on the printer's list, and a browser cannot read it out of a PDF: the file will say a typeface is called Garamond without saying whether Garamond travelled with it. Check that in the previewer before you publish. It is the one gap, and it is better to say so than to imply the report is complete.

The bottom margin is also approximate, and always in the safe direction. Only the position of the lowest ink can be measured, and the last line of a page rarely sits exactly on the margin, so the figure reported is never smaller than the truth. The inside, outside and top margins, the ones files are actually rejected for, are exact.

A scanned interior has no text to measure at all, and the checker says so rather than reporting margins of zero. If that is what you have, the interior is a picture of a book and no margin check will save it.

A file that passes is not a book that sells

Everything here is mechanical. It tells you the file will be accepted; it does not tell you the book is worth opening. Passing every check and still looking like a manuscript in a PDF wrapper is entirely possible, and common.

The difference is design: a chapter opener that signals a new chapter, running heads that help a reader place themselves, type set at a size and measure meant for paper rather than for a screen. Designrr builds that side of it, turning your content into a laid-out book with templates, a cover designer and an automatic contents page, so the file you check here is one worth printing.