"Provided a text document with specific fonts" is doing a lot of heavy lifting here.

Pretty much by definition, text documents don't supply fonts. So, reading text documents is still fine, unless your OS "helpfully" opens text documents using rich text viewers, in which case: please talk to your OS vendor.

For rich text documents, say PDF, the risk of personalized-and-or-remote embedded fonts is not exactly new. Maybe this variant is, but the general idea definitely isn't.

So, this, to me, is at best a possibly-novel "how to do DRM with PDF" technique. Which is interesting, but not exactly earth-shattering.

Or am I missing something here?