Adobe officially ended support for Reader XI in October 2017 . It no longer receives security updates or bug fixes, making your system vulnerable to malware via malicious PDF files.
This final patch addressed critical security vulnerabilities and stability issues before the product was permanently retired. adobe reader xi update
Many users and small business owners mistakenly believe that "if it isn't broken, don't fix it." This is a dangerous mindset when it comes to PDF software. Since the final Adobe Reader XI update in 2017, security researchers have discovered in older PDF rendering engines. These include: Adobe officially ended support for Reader XI in October 2017