Keep getting prompt to buy Acrobat DC

I just transferred all my files to a MacBook Pro. When I try to open a PDF file in Acrobat XI, I get a prompt to buy or trial Acrobat DC. When I close the box, I get another prompt. The Acrobat XI files are on my computer. They are also on my other computer but I only use Acrobat on 1 computer at once, which I understand is allowable. According to sales, Acrobat XI should work on my new computer and suggested I ask for help on the form.