this is tricky but not impossible.
First you need to know the full somExpression of your date field.
Open the form in Acrobat, your field will be populated with a date.
Now open the JS Console (Ctrl + J) and erase the populated value.
Type the following line into the console and confirm with the return button:
this.xfa.form.form1.Page1.DateField1.rawValue = null;
The syntax always starts with
followed by the somExpression of the target object.
In my example it is
Now, your field is cleared and you can apply the Reader Extensions from Acrobats menu.
I was unable to to see any values in the JS console, I took a closer look at the live cycle form and there was some java code that I think isn't doing anything and Formcalc is what is being used when I look at the script ediitor in live cycle. Is there a way around it with formcalc or should I change it to java?
The language you use to populate the date has nothing to do with that, so you can stay with FormCalc.
In fact you propably don't have to change anything in your form.
All you have to do happens in Acrobat, because here you're add the Reader Extenstions.
In Designer only check the somExpression of your date field.
In this case it's Form1.Page1.DateField1.
In Acrobat open the JS Console.
Type the full reference expression into the console plus the new Value it should have, such as "null".
this.xfa.form.Form1.Page1.DateField1.rawValue = null;
Press Ctrl + Return to execute that code.
The date field will be cleared immediately.
Now apply the Reader Extensions from Acrobat's menu.