Download a non-subscription Adobe Acrobat product

I want to purchase and download a standard version of Acrobat - I have used Standard (XI or IX - not sure) and want to purchase it for home use .  I can't find any option to do this without already having a serial number.  Can someone help?  This is also my first venture into a forum, and I'm not at all sure that I can access any answer I might receive - I hope it delivers to the email address I've registered with.