I posted about this issue back on 10/27/15 after I bought the classic track. I was able to get a refund and will buy the classic track when and if it is ever a fully functioning program. They need to let people know on the website before they purchase the classic track version.
WARNING: Acrobat Pro DC Classic (Standalone) Does Not Have Multi Tab Interface: Just to let people know that Acrobat Pro DC Classic Version (standalone) does not include the tabbed interface for multiple PDF file viewing in the same application window. Basically it is the same as X or XI standalone then. You have to buy the monthly subscription to get the tabbed interface. They say someday there may be an update to include the tabbed interface. Key word = someday. The web site does not tell you this. When you download the trial version you get the tabbed interface - but it is not a true demo for the standalone version - beware. $449.00 or $199.00 upgrade and you don't get a full working version of the product as you see on the website or with the demo. I just spent hours and hours with Acrobat Support including two remote access sessions to finally find this out. Reader DC does have the tab interface and it is free. So save your money for now if the Tabbed Interface is important to you."