When I open a webpage as a PDF in Books, the links don't work.

Alternatively you could try a website to pdf converter app.. and another method is to do share, then print, then when the preview comes up if you view that as full screen (by pinching and zooming in) tap share and open in books. If this doesn’t come up then you could save it as a pdf in files, then open it in books from the files app.

This method is a lot more longwinded.

Annotate and save a webpage as a PDF in Safari on iPhone

In the Safari app You can mark up a webpage, highlight your favorite parts, draw and write notes, and share your document as a PDF with others.

1. Tap .
2. Tap Markup , then use the tools to annotate the webpage.
3. Tap Done, then follow the onscreen instructions to save the page as a PDF.