Question

How to export the value of isVerified flag and check if the document was verified or not?

Answer

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.