This event is the first one that initiates after the form opens in Acrobat or Adobe Reader. Any calculation or scripting tasks that require the full form, or that should only run once when the form filler first opens the form, should use this event. For example, you can use the docReady event to check the version of Acrobat or Adobe Reader and return a message to the form filler if the form filler must upgrade the application before filling the form.
See also 

docReady event