Note: Adobe has moved heavily toward subscription models. If you have a redemption code (usually purchased from a retailer like Amazon or Best Buy), you may first need to convert the redemption code into a serial number via the Adobe website.
Convert Acrobat Pro trial to a full license - Adobe Help Center how to activate adobe acrobat pro license key
If you have already installed a trial or the software is asking for a key upon launch: Note: Adobe has moved heavily toward subscription models