1. First off, you will need "Installshield 2012 Spring" version or newer.
  2. Select New Kill Process
  3. If you select Immediate Executionthen add the following property to the Property Table
    1. ISTerminateProcesses
    2. Value is ProcessName or Process ID "acrobat.exe" or 1022
  4. If you select Deferred Execution then add the name of your CustomAction to the Property Table
  5. Here is the Property Table..
  6. Last step, add it to the Sequence. (remember, if your adding as Deferred System Context, then make sure it happens between InstallInitialize and InstallFinalize.