You can choose a flattener preset in the Print dialog box, or in the format-specific dialog box that appears after the initial Export dialog box.
If you regularly export or print documents that contain transparency, you can automate the flattening process by saving flattener settings in a transparency flattener preset. You can then apply these settings when you print or export to PDF 1.3 (Acrobat 4.0), SVG, or EPS formats.