What's the risk case? If the author released a PDF, you reuse it under the GFDL and the author then sues you for copyright violation because you didn't keep to the "transparent copy" part of the licence terms, what judge wouldn't throw it out? That's a serious question. I suppose I should ask licensing@ really ...
Not sure, you might be able to use some stopel doctrine or unclean hands or whatever, but ask someone who has a clue, yes. :-)
--David.