Other journalists disagree: “I don’t know that journalists do “do this constantly”—I was always told that you get into legally questionable territory when you start asking for documents instead of just accepting them when offered.” https://twitter.com/yaelwrites/status/1116343757278892037?s=...

I would not be surprised to hear that Greenwald had done it, but that does not imply that it is actually common, nor legal.