why don't pdfs in books open in books? macOS 14.1. I want to read from books, not preview or acrobat.

Apple's Books application is designed to open EPUB style documents. If you ask it to open a PDF, it will add it to its "My books" and dutifully open the PDF in Preview, the default PDF reader. I have tested this with a variety of PDFs created by different tools, from different dates, and PDF versions. Books consistently hands them off to Preview for viewing. It is what Preview was designed to do.

This does not come as a surprise as PDFs are flat, binary documents with no internal EPUB standard folder hierarchy or styling content for guidance on how Books should navigate them. Preview opened correctly every single PDF that I asked Books to open.

I have tested Books on Mojave 10.14.6, Big Sur 11.7.10, Monterey 12.7.1, Ventura 13.6.1, Sonoma 14.1.1 and across several different PDF in all cases, Books added the PDF to itself and then opened it in Preview.

We are fellow users and cannot explain developer team rationale for this Books behavior, and the product teams do not participate here to answer that kind of question either.

More information is, well, necessary, as the PDF files I have access to will open in the Books app here. (Though also running macOS 13 Ventura, not macOS 14 Sonoma.)

Are these PDF files standard ones, or are these maybe something a little more special? Adobe extended the PDF format, and some of those extensions are not universally compatible, for instance.

Does Preview open the PDFs?

If the PDF is not encumbered, and is not sensitive, there is a PDF/A compliance tool here:

… http://www.validatepdfa.com/