Before you download, please be aware that Adobe ended support for Adobe Reader XI on October 15, 2017 . Version 11.0.23 was the last security update released for this product. Using this software on a machine connected to the internet may expose your system to unpatched vulnerabilities, as it does not receive new security fixes.
Adobe Reader XI (11.0.23): A Look Back at the Final Classic Version
Caution: Avoid third-party "download manager" sites. They often bundle adware. Always verify the digital signature of the file after downloading.
Unless you are running Windows XP on an air-gapped machine, you should install the current Adobe Acrobat Reader DC (or a lightweight alternative like Foxit or SumatraPDF). Using Reader XI on a modern, internet-connected PC is a significant security risk.