On October 15, 2017, Adobe ended technical support, product updates and security fixes for any version of Acrobat XI and Reader XI.
What does End of Support mean?
End of support means that Adobe no longer provides technical support, including product and/or security updates, for all derivatives of a product or product version (e.g., localized versions, minor upgrades, operating systems, dot and double-dot releases, and connector products).
What should I do now?
You may continue to use Acrobat XI and Reader XI, but Adobe will no longer provide any updates or address any existing bugs or security issues in the software.
Because of this, it is strongly recommended that you update to the latest versions of Adobe Acrobat DC and Adobe Acrobat Reader DC. This will ensure
that you benefit from all new functional enhancements and security updates, not to mention support for newer operating systems. Technical support for
Acrobat XI will also be discontinued.