At first glance an apparently straightforward question.   However, in practice it is not as obvious as you might think.  In the recent case of IBA Molecular Italy Srl v Azienda ULSS n. 3 and Others [c-606/17] the CJEU was asked to consider an arrangement whereby a contracting authority provided finance to an economic operator for the purposes of manufacturing medicinal products which the economic operator then provided free of charge to the contracting authority.  

The law was considered under the old 2004 Directive, but the same position would apply under the 2014 Directive and hence the PCR 2015.  The starting point is that a contract will only be caught by the PCR 2015 if it is a "contract for pecuniary interest ". 

The CJEU held that it is clear from the usual legal meaning of "for pecuniary interest"’ that those terms designate a contract by which each of the parties undertakes to provide a service in exchange for another.   Therefore a contract for the exchange of services is covered by the concept of a public contract.