Auto-Date

Hi, I have this script that is suppose to automatically put in the current date upon opening.
 
field properties box> calculate>
var f = this.getField("Today");
f.value = util.printd("mm/dd/yyyy", new Date());
 
The problem is, I can't find the Document Open or Page Open in Adobe 8 to be able to put the code in.
 
Does anyone know where this is, or if there is another script that can be used to put in an auto date?