When you say book, do you mean Book in the InDesign sense of a collection of individual documents collected together using the Book feature, or a single long document organized as chapters or similar?
If the former, I believe there is a bug and bookmarks after the first document do not work, which is perhaps what you are seeing. The only workaround I'm aware of is to fix them in Acrobat Pro, not Reader.
Thank you for your answer. Sorry for bothering everyone. I found where I am wrong. I simply exported the Book (yes it is a collection of individual documents collected together using the Book feature) as pdf Print and everything is fine.
Thank you again for taking your time. Regards!
That may work for you (I'm pretty sure the problem I remember is limited to PDF (interactive) exports), but there are some new twists to export for print and support for interactivity, notably buttons don't work, and there may be others as well -- I'm a print guy and don't deal much with interactive content -- so make sure the PDF does all the things you expect.