I have downloaded two audiobooks from Apple Books, both which have supplementary PDFs. Where on earth are they? They are not in the chapter menu, not in the PDF section of Books, not anywhere I can see on either iPhone or Mac. I have reported the issue to Apple twice to no avail.
6/29/23 I recently had (have) the same problem. I purchased several audiobooks. Months later, I could not find the pdf that came with the book(s). I searched every pdf in my whole Apple Books Library. Finally, I went into iTunes on my PC, signed into my account, found the audiobooks, opened up the order to expand the details, and then I hit the "Resend" button. That is where and how I found the pdf. Now I have to go back into each book, and follow the same steps as for the first one, so that I can find the rest of them. The actual pdf is inside the audiobook. If you open the Audiobook and look in the chapters section, on the bottom, under the volume slider to your right hand side, there are lines going across which represent the chapters. If you tap on the lines, you will see a message that reads: "View PDF Content". Tap on that and it should bring up the PDF file right into your Apple Books Library. As I am typing this, I am also checking the rest of my audiobooks. So far I only see one pdf out of 4 that I hit the "Resend" button on. So, it looks like I will have to keep trying until I see all the PDF files for all my Apple Audiobooks. Good luck!
Apple Books Audio supplementary PDF
