This month Adobe implemented a new program that aims to provide a regular schedule for patches (similar to Microsoft's Patch Tuesday) in order to keep vulnerabilities to a minimum.
The first quarterly patch goes to Adobe Reader and Adobe Acrobat. This new version patches critical security vulnerabilities that crash the programs (Reader and Acrobat) and can allow an attacker to gain access to your PC.
Download Adobe Reader 9.1.2.
If you'd like to read about the details of the vulnerabilities, read Security Bulletin APSB09-07.