Its unfortunate, Emilio that you don't have an Apple device as the Apple books version has Hyperlinks built in to the script allowing you to jump back and forth through the book to associated topics. This forum only allows file sizes of 0.98 MB as attachments and the pdf file for version 2, as yet unpublished at 24 double pages, is over 38 MBs so I do not know how to help you.
I recently deleted my Dropbox account as I found that I wasn't using it, as I sent large files directly with Apple Mail Drop This is done via email without having to post the file to the cloud and then sending a link; however this requires an email address.