From Tracker Software PDF SDK
Gets visibility state of UI-pane.
HRESULT GetPaneVisibility2([in] LONG nPaneID, [out, retval] LONG* nVal);
- [in] The unique identifier of UI-pane.
- [out, retval] Returns visibility state. The supported values:
- 1 - is visible;
- 0 - is invisible, because is overlapped by other panes;
- -1 - is hidden permanently;
Returns S_OK if operation was successful or error code in other cases.