Why the PDF must close on a signature count (and where the blank pages come from)
The press prints in 4s (sometimes 16s). The real count appears after images and the TOC. Extra pages are not a mistake: they close the signature.
A paper book has two sides per leaf. The press also does not print “one page”: it prints a signature. On Amazon KDP, IngramSpark, and most digital POD that signature is 4 pages: one sheet, both sides, folded once. Offset novels are often 16. If the interior lands at 74, that is already even (the book can exist), but 74 is not a multiple of 4: 2 pages are left over. Either the plant or the factory must add them.
You cannot guess that number when you upload Word. It moves when photos inject, when the TOC takes a leaf, when a chapter is pushed to the right. Signature close therefore sits after you generate the preview, next to the page-count and spine spec — not at the start, with trim size.
One radio: signature of 4 (KDP, Ingram, POD) or 16 (offset novel). The factory counts how many pages are missing to the next multiple and appends them at the end. Path D’s spine uses that total, not the earlier 74.
Those extra leaves are yours. They can stay blank or carry finished images (another title, a sponsor, a portrait) only on odd (recto) pages, full page. The even verso stays blank. What you should not do is leave the gap for Ingram or KDP to fill: they pad too, and then the cover spine no longer matches the printed block.
IngramSpark’s guide says not to pad, and that they will add a manufacturing / barcode leaf. If you upload to Ingram, 4 is usually enough and an even count already stores. Still, if your PDF already closes on 76, 80, or 84, the spec sheet and the jacket speak the same number. For offset, ask the signature: if they say 16, the file must land on 80, 96, 112…