The Adobe® Acrobat® and Reader® 8.1.6 update addresses several security vulnerabilities. Please see Security Bulletin APSB09-07 for details. Adobe always recommends that you install the latest updates.
The Windows® update includes the changes made in Adobe Acrobat and Reader 8.1.4 and 8.1.5 updates. Thus if you have Acrobat or Reader 8.1.3 on Windows installed, you can directly update to 8.1.6 without installing either 8.1.4 and 8.1.5 first. Or, if you have Acrobat or Reader 8.1.4 on Windows installed, you can update to 8.1.6 without installing 8.1.5 first.
Adobe Acrobat or Reader 8.1.6 cannot be applied to a 8.1.4 or 8.1.5 AIP or a system where the application was installed using a 8.1.4 or 8.1.5 AIP. If the system was updated to 8.1.4 or 8.1.5 by running a patch then running the 8.1.6 patch will cause the system to be successfully updated.