Adobe Acrobat Reader XI (11) was released in 2012 and represented a significant milestone in the history of the PDF viewer. Before the advent of the "Continuous" track (the modern, auto-updating Creative Cloud era), major versions like 9, 10, and 11 were distinct releases that remained static until the next major iteration.
If your sole goal is reading PDFs on a legacy machine, consider these safer options before resorting to an unsupported Adobe build: adobe acrobat reader xi 11.0.23 download
Supports Elliptic Curve Cryptography for more secure digital document signing. JavaScript Control: Adobe Acrobat Reader XI (11) was released in
Adobe does not keep old versions on their public homepage, but they do maintain a hidden, official FTP archive. JavaScript Control: Adobe does not keep old versions
If you only need to on an old machine, consider using a lightweight, still-supported alternative instead of an abandoned Adobe product: