It is incremental.
This update requires that Adobe Reader 9.3.3 is installed on your system. To determine which version of Reader you have currently installed, choose Help> About Adobe Reader.
If you have version 9.3.3 installed, download and install the incremental patch.
It is incremental. But, this does not necessarily means if let's say you are on 9.3.1, then you have to undertake separate actions to first get to 9.3.2, then 9.3.3 and finally 9.3.4. Contrarily, let's say you are on 9.3.0 version. Now, just run "Help > Check for updates" within Adobe Reader and the Adobe release manager will take you to 9.3.4 (latest version) by downloading and installing all the intermediate patches for you automatically.
The 9.3.4 patch is an incremental patch, and can only be applied on Reader 9.3.3. or Acrobat 9.3.3.
You can obtain the Reader 9.3.3 chained installer from: ftp://ftp.adobe.com/pub/adobe/reader/win/9.x/9.3.3/
Only after installing Reader 9.3.3, can you apply the 9.3.4 patch.
Alternately, you can perform a Help>Check for Updates operation, anytime from Reader 9.2.0 onwards, which will aid you in installing Reader 9.3.4 in a single go by installing patches sequentially by itself.