I'm trying to create an IF field in a mail merge to display one of two
paragraphs depending on whether the Date of Birth field in a record is after
a certain time. I've tried using:

{ IF { MERGEFIELD Date_Of_Birth } 01/07/1976 "Text1" "Text2" }

(The date format above is UK, i.e. dd/MM/yyyy)

....but Word always seems to treat the date as a number, and so any date
later than the first of a month counts as a positive, irrespective of month
or year.