Application events initiate as a result of the actions that a client application or a server application perform, either due to a form filler action or an automated process. Application events do not exist as part of a general flow of events. They are single events that correspond to actions that the client or server application performs.
If a form filler saves the form in Acrobat or Adobe Reader, the preSave event initiates immediately before the save operation, followed by the calculate, validate, and layout:ready events, in that sequence for all objects on the form. The same event sequence initiates if the form contains a script that programmatically saves the form.