From Adobe Systems:
Adobe Reader Update updates security and improves functionality. Updates safeguard your system against malicious attacks through PDF files. Why so many updates? Because PDFs are used so universally, they can be a target for hackers. Adobe provides regular updates to safeguard your computer from attacks. If you've gotten multiple update messages, make sure the last update fully installed. Some browsers download to a separate update window. In these browsers, double-click the Reader or Acrobat file to complete the installation.
What's new in this version:
Version 11.0.05 fixes specific security issues.