True if merge field names are displayed in a mail merge publication; False if information from the current data record is displayed. Read/write Boolean.
expression.ViewMailMergeFieldCodes
expression Required. An expression that returns one of the objects in the Applies To list.
If the active publication isn't a mail merge publication, using this property has no effect.
This example hides the mail merge field codes in the active publication.
ActiveDocument.MailMerge.ViewMailMergeFieldCodes = False