Use approval workflow data in MS Word

I need to put approval workflow data in Word documents. I learned to put the version number by using the Label Quick Part in Word and an information management policy in the library to set the Label to the version number (_UIVersionString).

This works ok, but I need to show in the document also the approval date. I am using the Publishing Approval workflow in a subsite. I have seen that there is a Quick Part in Word named Publish Date but it looks that it is always empty.

How can I add the approval date to the document so it is automatically shown as with the version?

Thanks!