Just to add a quick note to what a.l.e has said, if you're getting the magazine professionally printed then you need to make sure that the software you use to merge the PDFs won't destroy anything like printer marks, colour management, etc.
This is out of my field of expertise but I've heard that some software "mashes" the PDFs together in the simplest way possible and some stuff goes missing. It's something to keep in mind before you look to get it printed.
Maybe someone with printing experience can explain this a bit better. Or maybe your print shop can advise. (There's a chance that you could send them the individual parts and they'll stitch them together for you.)