Add and remove layers
Using
the Layers panel, you can add new layers, add new sublayers, delete unwanted
layers, and duplicate existing layers and objects.
Add a layer
A blank layer is inserted above the currently selected
layer and becomes the active layer.
Do one of the following:
Click the New/Duplicate
Layer button 
.
Select Edit > Insert > Layer.
Select New Layer or New Sub Layer from the Layers panel Options
menu or pop-up menu, and click OK.
Delete a layer
The layer above the deleted one becomes the active layer.
If the deleted layer is the last one remaining, a new empty layer
is created.
Do one of the following:
Drag the layer
to the trash can icon 
in
the Layers panel.
Select the layer and click the trash can icon in the Layers
panel.
Select the layer and choose Delete Layer from the Layers
panel Options menu or pop-up menu.
Duplicate a layer and objects
A duplicate
layer contains the same objects as the currently selected one. Duplicated
objects retain the opacity and blending mode of the original objects.
You can change the duplicated objects without affecting the originals.
Do one of the following:
Drag a layer to
the New/Duplicate Layer button.
Select a layer and choose Duplicate Layer from the Layers
panel Options menu or pop-up menu. Then select the number of duplicate
layers to insert and where to place them in the stacking order.
Because the Web Layer is always the top layer, the At The Top option
means just below the Web Layer.
Alt-drag (Windows) or Option-drag (Mac OS) a layer.
Duplicate an object
Alt-drag (Windows) or Option-drag (Mac OS) an object.
PDF (adobe.com)
