DesktopAndNetStandard.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Library</OutputType>
    <TargetFrameworks>net45;net40;net40-client;netstandard1.5</TargetFrameworks>
  </PropertyGroup>
  <PropertyGroup Condition="'$(TargetFramework)' != 'netstandard1.5'">
    <DefineConstants>$(DefineConstants);DESKTOP</DefineConstants>
  </PropertyGroup>
  <PropertyGroup Condition="'$(TargetFramework)' == 'net40-client'">
    <!-- TargetFrameworkInference does not support net40-client -->
    <TargetFrameworkIdentifier>.NETFramework</TargetFrameworkIdentifier>
    <TargetFrameworkVersion>v4.0</TargetFrameworkVersion>
    <TargetFrameworkProfile>Client</TargetFrameworkProfile>
  </PropertyGroup>
  <ItemGroup Condition="'$(TargetFramework)' != 'netstandard1.5'">
    <Reference Include="System.Windows.Forms" />
    <PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
  </ItemGroup>  
  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.5'">
    <PackageReference Include="Newtonsoft.Json" Version="9.0.1" />
  </ItemGroup>
</Project>