Lock Automatic Date Field after Submit

Question

I have a form that generates the current date when the form is open.  Once the user complete the form I have a submit button that will flatten the file and submit the completed PDF. All this works great. 
The challenge I have is even though the form is flattened, when a user opens the flattened PDF in a PDF Reader the date displays the current date.  Is there a way to set this field to update only once when the form is initially opened?
I am currently using the following function to generate the date in the field.
var f = this.getField("OpenDate");
f.value = util.printd("yyyy/mm/dd", new Date());
I am running Adobe Acrobat X Pro.
Regards,
Robert

Answer 1

To test the form, you need to close the saved form and reopen it. Because the field is empty it should populate. If you save, close the form, and reopen the form the date should not change.
Note the PDF needs to be opened before a document level function will execute and it will only execute once.
If you want the form to work for others, it needs to be saved with  the date field empty because when the form is opened and the document level script runs it will only populate an empty date field and if the field has any non-null value in it the field will not update.
For testing you could change the script to include an alert to tell you if the date field is being updated or not.
A "flattened" PDF has no form fields.