I don't know whether boundaries have been redrawn, but this document is French rather than Belgian, and your hoped-for date is about 100 years too early.
The date is given in lines 3 and 4 according to the French Revolutionary Calendar:
Du vingt-huit jour du mois de messidor
l'an dix de la République françaiseThere are various online calculators which will translate this to what the rest of Europe was using; the easiest one I found was at
https://stevemorse.org/jcal/french.htmlEnter the year (dix = 10), month (messidor) and day (vingt-huit = 28), and it gives 17 July 1802.
You can read more about the calendar, and find tables for working out the date manually, at
https://en.wikipedia.org/wiki/French_Republican_calendar