Work on fixed installations (faste installationer) has to be done by an autoriseret elinstallatørvirksomhed (authorised electrical firm). Ask whether they hold the authorisation themselves or bring someone who does, and get that on the invoice.
Silkeborg is lakes and forest. Many houses sit on a slope, with trees and poor access for a van. Garden, drainage and terrace work sit beside ordinary building jobs. The same 4 businesses as the Danish page: BYENS EL ApS, EL-GÅRDEN A/S, KRAGELUND EL A/S, Silkeborg El-Service ApS.