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I guess it depends on what you need it for.

If I just want to hear such a song once there's a good chance it's on YouTube somewhere.

Do you want to add this song to your Apple Music Library? It's more complicated and there are legalities that have to be addressed…or ignored.
 
I want to add it to the music I play for the holiday season.
 
Yes, what was formerly known as iTunes. If I remember right, it was in iTunes several years ago, before the Airs came out and Apple Music was introduced. Funny thing is, I can find it in the finder app and can play it, but I can't add it to my Apple Music library.
 
The first question is: What is the file format for that song?

I don't know if the Apple Music service has the ability to block some content from being uploaded.

There are some formats that aren't compatible.
 
I was just about to reply back here. I have it added and if I remember correctly, all I had to do was go to the finder, find the file, and drag and drop to the Apple Music library.
 
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