My Adobe Acrobat XI that I purchased no longer works on my MACBOOK PRO (OS X El Capitain 10.11.6. When I try to open a PDF it takes me to a screen asking me to Buy Acrobat DC. I do not want to buy Acrobat DC but just want my Acrobat XI to resume work

Can anyone suggest how fix ACROBAT PRO XI on my Macbookpro. My Adobe Acrobat Pro XI that I purchased no longer works on my MACBOOK PRO (OS X El Capitain 10.11.6. When I try to open a PDF it takes me to a screen thanking me for trying the trial version and asking me to Buy Acrobat DC. I already bought Acrobat Pro XI and do not want to buy Acrobat DC. I just want my Acrobat Pro XI to resume working. The answer on a prior discussion DOES NOT provide an answer, it only asks the same question.