How to export the value of isVerified flag and check if the document was verified or not?
Add the following script to the After document state changed event handler:
if(Document.IsVerified == true)
Document.Field("Invoice Layout\\Field").Text = "Verified";
Where Invoice Layout\\Field is the link to the required field in which the value should appear.
So, if the document was verified, the field will contain the value Verified.