Oooh, I think I know what happened. The "Buy now" button only appears under updates and devlogs. On the main page, it is hidden by default—since I configured two different "packages" you can get, there's no standard buy button to avoid confusion (well, that was the intent, I didn't know itch would still show it on other pages).
If you didn't purchase it yet, go to the main product page and choose the PDF bundle from there. If you already did but can't access the files, drop me an e-mail at capacle@gmail.com and I'll send you a download key. Thanks and sorry for the trouble.