Shop website URL (https://…) when you have one. Or mailto:/email — opens Gmail compose in the browser (same as Contact).
If checked, the book button reads “Donate · PDF”. Leave unchecked if this title has no PDF offer.
Leave empty or 0 for unlimited. A positive number limits how many people can read this book online at once.
Only applies when copies are limited. Blank = default 12. 0 = no free preview (seat required from page 1). Positive = first N pages free without a seat.