So are you telling us that farmers put their produce on to their own lorry and just drive to the Continent at a whim ?In either of your replies you have not considered the thousands of small businesses and farmer who trade with the EU who have never had to do anymore than a shipping invoice/airway bill and not much else. Of course, many exporters will probably go out of business once their goods are subject to the addition of a tariff when landing in the EU.
If so then "yes", he may have to look up the EU forms to fill in.
But I suspect the farmer uses a haulier - who only has to find the forms once - for all his farming customers.
And there is no certainty of EU import tariffs - if the EU agrees to WTO Article 24 (zero tariffs during negotiations).