Since Adobe no longer hosts Acrobat XI updates on its main download pages, you have two legal options:
It is important to note that Adobe officially ended "End of Life" (EOL) support for Acrobat XI on October 15, 2017. While the 11.0.27 patch is the most secure version of the XI series, it does not protect against vulnerabilities discovered after its release date. adobe acrobat xi pro 11027 patch hot
Installing the Adobe Acrobat XI Pro 11027 patch hotfix is a straightforward process: Since Adobe no longer hosts Acrobat XI updates