An enterprise that wishes to place a product on the market in Denmark must apply for authorisation from the Danish Environmental Protection Agency. This applies irrespective of whether you are a producer, an importer or a distributor.
In many cases it is incumbent on producers or importers reselling to other companies to submit applications for product authorisation. The responsibility can also rest with the enterprise that imports and uses the product or sells the product directly to consumers.
Enterprises that exclusively use - and therefore do not produce, import or sell - the biocidal product only have one obligation in relation to the legislation. That obligation is to ensure that the biocidal products they use may lawfully be placed on the market in Denmark. Ask the supplier.