PDF (adobe.com)

Optimize by using a preset option

Choose Window Optimize to open the Optimize panel. When you choose a preset option, the rest of the options in the Optimize panel are set for you.

 Select a preset option from the Settings pop-up menu in the Property inspector or the Optimize panel.
GIF Web 216
Forces all colors to web-safe colors. The color palette contains up to 216 colors.

GIF WebSnap 256
Converts colors to their closest web-safe color. The color palette contains up to a maximum of 256 colors.

GIF WebSnap 128
Converts colors to their closest web-safe color. The color palette contains up to 128 colors.

GIF Adaptive 256
Contains only the actual colors used in the graphic. The color palette contains up to a maximum of 256 colors.

JPEG – Better Quality
Sets quality to 80 and smoothing to 0, resulting in a high-quality but larger graphic.

JPEG – Smaller File
Sets quality to 60 and smoothing to 2, resulting in a graphic less than half the size of a Better Quality JPEG but with reduced quality.

Animated GIF WebSnap 128
Sets the file format to Animated GIF and converts colors to their closest web-safe color. The color palette contains up to 128 colors.