I'm not sure if you're... into newspaper lingo.

But "anonymous source" usually means "Dude who emails reporter", and often someone who is an executive level or above. You know, someone who matters, but for their own sake they need to stay anonymous.

If its just a document, then the "source is the document". You don't need to quote an anonymous person (who likely has their own biases), you just quote the document itself.

These words that journalists use? They have meaning. "Anonymous source" is not how the story is described. It is described, rather precisely, as "internal documents".