Thanks for all your suggestions. I still haven’t found a reliable way to bring down the size of the PDF under 10MB; I get it after much fumbling and hit & miss. The interactive option is interesting but gave me a 19,5MB PDF, better than the 25MB from the Print option but not good enough. The closest I came to my target was with a copy for the web (RGB colors, jpeg images, replacing any drow shadow effect with a gray box, etc.), but that PDF was still around 13MB. I optimized that last one in Acrobat and after a few tries brought it down to 9,8MB, with quite pitiful results on the images, but that’s what the client wants… and offering the mag in two parts will be the very last resort (quite sure that option will be refused).
By the way, I had to uninstall Acrobat DC and go back to my old Acrobat X; all the links in any file I tested stopped working, and after a full day trying to get that feature going again I gave up. Anybody else encountered a similar problem? It used to work correctly; hovering above a link still shows the address, right-clicking on the link give me the usual menu, but no amount of cllcking or choosing to open the link from the contextual menu has any effect. Looks like the latest update of OS X (Yosemite 10.10.5) or, more likely, Acrobat DC, is interfering with the activation of the links. Security feature?