looks like it's actually one-to-many across unicode, if so then you could think of it as approaching one-time-pad encryption, with the key being the font
if the generator crafted a new font every time, never used the same codepoint twice, and kept the font separate from the document (pre-shared by being installed on the intended receiver's machine) then it'd be uncrackable!
if the generator crafted a new font every time, never used the same codepoint twice, and kept the font separate from the document (pre-shared by being installed on the intended receiver's machine) then it'd be uncrackable!