Cantharis obscura and Canthara paradoxa are two soldier beetle species that are very similar and can not be told apart from each other without detailed research.
However, Cantharis obscura is quite common in the Netherlands while Cantharis paradoxa is quite rare.
Cantharis obscura and Canthara paradoxa can easily be confused with Cantharis fusca.
The main difference is that Cantharis fusca's first segments of the antennae are yellow/reddish while the first segments of the antennae of Cantharis obscura and Canthara paradoxa are black above and yellow below (clearly shown on the photo).

It flew into my car! Hilversum, The Netherlands, 12 May 2013