Adobe officially ended support for all Acrobat XI products on October 15, 2017 Update 11.0.23:
This version addressed specific functional bugs alongside security patches: Accessibility: Download Adobe Acrobat Xi Pro 11.0.23 Fixed
Although support had ended, this final "planned update" was released shortly after to provide critical security mitigations (APSB17-36) and bug fixes. Usage Risk: Adobe officially ended support for all Acrobat XI