After you update to Adobe Acrobat 8.1.2 on Mac OSthe droplet feature stops working. This issue does not affect Acrobat Professional on Windows.
For more information about this issue, see "Color conversion issues when converting to PDF/X-3 in preflight (Acrobat 8 Professional, and Acrobat 3D 8 on Windows and Mac)" (TechNote kb402541).
Keywords:
kb403208

