I don't think it's unreasonable to think that a well-funded team of computational linguists could come up with enough equivalent grammatical/synonym permutations to render a very large number of versions of text.
Two problems: 1: When outlets learn this is the case, they just make sure never to publish the exact phrasing of any such leaked document. 2: This only helps you track down the leaker, not prevent him from leaking. The "phone home" document would presumably catch the leaker as he's collecting the documents.
Two problems: 1: When outlets learn this is the case, they just make sure never to publish the exact phrasing of any such leaked document. 2: This only helps you track down the leaker, not prevent him from leaking. The "phone home" document would presumably catch the leaker as he's collecting the documents.