The PdfWidgetAnnotation, PdfPage, PdfDocument ,or PdfField include a property named AdditionalAction that specifies an additional-actions that extends the set of events that can trigger the execution of an action.
The AnnotationPageOpen and AnnotationPageClose trigger events in the PdfAnnotationLevelActions have a similar function to the PageOpened and PageClosed in the PdfPageLevelActions class. However, associating these triggers with annotations allows annotation objects to be self-contained and greatly simplifies authoring. For example, annotations containing such actions can be copied or moved between pages without requiring page open/close actions to be changed.
The AnnotationPageVisible and AnnotationPageInvisible trigger events allow a distinction between pages that are open and pages that are visible. At any one time, only a single page is considered open in the viewer application, while more than one page may be visible, depending on the page layout.
For these trigger events, the values of the PdfAnnotationFlags have no bearing on whether a given trigger event occurs.