How to make a nuspec (.NETFramework) to install a legacy dll so that it is copied along with the assembly in the build folder

Question

I try to create a nuspec file to distribute de .NET component usiing a legacy DLL. Here's an extract of the nuspec file.

My problem is I can't figure out how to specify the legacy dll so that it is copied to the "build" folder when compiling a project using my .NET component.

With nuget when deployiong an assembly that one is copied from the packages... folder to the build (debug or release) folder. I want the same for my legacy dll so that I can run the program using my assembly using the legacy dll. I could copy the file within the build but it doesn't make sense, nuget should be there for that.After having searched a loy I inserted a "references" item in the nuspec but when specifying the "file" entry for my legacy dll (AAA.dll) I don't know what to put in target. I've tried ref\any, ref\net47, lib, lib\any, lib\net47 (that one simply prevents the package to install becaus eit tries to reference AAA.dll in the project),...

<package>
  <metadata>
    <dependencies>
      <group targetFramework=".NETFramework4.7">
      </group>
    </dependencies>
    <references>
      <group targetFramework="net47">
        <reference file="AAA.dll" />
      </group>
    </references>
  </metadata>
  <files>
    <file src=".\Release\ASSEMBLY.dll" target="lib\net47"></file>
    <file src=".\Release\AAA.dll" target="lib"></file>
  </files>
</package>

What I want is: when compiling AAA.dll should be put in the build folder as ASSEMBLY.dll is, so that the program using the assembly dll (using my legacy dll) does not crash.

I could not find a working solution on Internet and I turn to you for that.

UPDATE I finally managed to do it but had to do it wit the following steps (even though not all may be necessary, that's the way I did it).

1. Move my package to PackageReference format
2. created a .targets file with the exact same name as my package (i.e. my.package.I.created.targets). That targets file is located in my project folder, next to the csproj file and its content is:

    <?xml version="1.0" encoding="utf-8"?>
    <Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
      <ItemGroup>
        <NativeLibs Include="$(MSBuildThisFileDirectory)**\mydll.dll" />
        <None Include="@(NativeLibs)">
          <Link>%(RecursiveDir)%(FileName)%(Extension)</Link>
          <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
        </None>
      </ItemGroup>
    </Project>

3. Inside the csproj file I added the following lines:

    <ItemGroup>
      <None Include="$(SolutionDir)$(Configuration)/mydll.dll" Pack="true" PackagePath="build\">
        <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
      </None>
      <None Include="$(SolutionDir)/my.package.I.created.targets" Pack="true" PackagePath="build\">
        <CopyToOutputDirectory>Always</CopyToOutputDirectory>
      </None>
    </ItemGroup>

The result is:

• the legacy dll is inserted into the nupkg
• the legacy dll is copied into the target folder along with the assembly when that one is referenced