How I could copy drop shadow to another object?
If you click on the 'Copy shadow properties' button on the drop-shadow toolbar you'll get a large arrow appear. If you click this arrow on the existing drop shadow and then on the object you want to copy the shadow to it should appear (although in my experience this can be very fiddly with small drop shadows).
The other way is to save an existing drop shadow as a preset and then keep using this as long as you need it.
thank you very much ,it is too helpful