public class DocumentResult
{
    public DocumentResult()
    {
    }

    public FooViewModel { get; set; }
}

public class FooViewModel{
    public string CompanyCode { get; set; }
    public DateTime RegistrationDate { get; set; }
}

[ServiceContract]
[DataContractFormatAttribute]
public interface IDocuments
{
        [OperationContract]
        [WebGet(UriTemplate = "/{companyCode}/{documentId}/docdetail", ResponseFormat = WebMessageFormat.Json)]
        DocumentResult GetDocument(string companyCode, string documentId);
}

public class Documents : IDocuments
{
    public DocumentResult GetDocument(string companyCode, string documentId)
    {
        // breakpoint here
        ...
    }
}