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Function Reference
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PDF supports the following application events which can be used to control the visibility of an OCG
or layer:
Each event has corresponding categories or members in the Content Usage dictionary as well as
additional categories, which can be combined with three events, e.g. the viewer language or the
current user.
A viewer, that supports these application events, will change the visibility state according to the
settings in the Content Usage dictionary.
Note that application events are not supported in all viewer applications. If a watermark should
appear when printing, for example, then it is usually best to set the state of such a layer to visible,
and to make it invisible in the View event. A viewer that supports application events will hide the
layer at viewing time but still print it. A viewer that does not support application events will always
display the layer.
If the initial state of the layer would be invisible, then it would also stay invisible at printing time if
the viewer does not support application events but layers.
Return values:
If the function succeeds the return value is 1. If the function fails the return value is 0.

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