As stated in the
Adobe Support Lifecycle Policy, Adobe provides five years of product support, starting from the general availability date of Adobe Reader and Adobe Acrobat. In line with this policy, support for Adobe Acrobat Classic 2015 and Adobe Acrobat Reader Classic 2015 ended on April 07, 2020.
Adobe strongly recommends that you update to the latest versions of
Adobe Acrobat DC and
Adobe Acrobat Reader DC. By updating installations to the latest versions, you benefit from the latest functional enhancements and improved security measures.