I find lots of ways to auto fill today's date in a pdf form. How do I lock that date so that when the file is reopened the date does not change?
This is tricky since you have to distribute the form with the date field field empty.
If all users will have Acrobat, you could have a script that disables the function to fill-in the date.
For Reader, you need to test the field for the date to be empty and if it is then populate that field.