Hardcover or paperback: hinge and wrap
The interior can share trim. The hardcover jacket is larger: board, hinge, and wrap that glues inside. You pick that on Path D.
Paperback is the flexible cover that wraps the page block: back, spine, front, a little bleed. Hardcover (casebound) is board covered by wrap that folds inside. There is also paperback with flaps and hardcover with a dust jacket. The interior — the page PDF — can share trim. The outside file cannot.
If you reuse the paperback PDF for hardcover, the spine is short (the board is missing), the hinges do not exist in the file, and the wrap cannot glue inside. KDP hardcover guides are full of that mistake. On Path D you pick the kind: paperback, paperback with flaps, hardcover, hardcover with jacket. The mold changes. The hardcover spine is the page block plus 0.06 inches of board. There is a hinge (0.375 inches) and wrap with more bleed (0.625). You do not measure that with a ruler on the table; you pick it from the list.
The interior comes first, on Path A, B, or C, at the trim you want (text sizes on A/B; album sizes on C). The spec gives you pages and block spine. Path D reads that spec. If there is no interior yet, you can type trim, paper, and pages by hand, but the number must be the real one, signature included.
Flaps: if you ask for them, the wrap grows (about 3.5 inches by default, with a minimum). A blurb or an author portrait can live there. The barcode stays on the back, away from the hardcover hinge. This site does not sell ISBNs.
Colour and download: same as the interior, the jacket can be RGB or the CMYK they asked for. One session; do not close the tab. And do not stretch a paperback wrap in Photoshop “a little” so it looks hardcover. Generate again on D with the right kind.
Do it in the factory
