1script - 7:02 pm on Feb 28, 2013 (gmt 0)
Thanks, lucy24. Yes, I'll be starting sending X-Robots-Tag: noindex right away to make sure they are deindexed before I start redirecting them, just to avoid any possible cloaking issues.
As far as similarity to image hotlinking protection, I think it's *exactly* like hotlinking because many (most?) people have PDF plugins in their browsers that open them inside browsers and also inside frames. I haven't seen it done to my PDFs (and perhaps I just didn't look hard enough) but there are sites that do exactly that - they rank for the KWs found in the titles of your PDF but when you open their site, there would be a frameset where one frame is *their* ads and another is *your* PDF. Your wasted bandwidth, their ads revenue.
So, yes, I think this PDF redirection thing is pretty clearly needed. After that my next step would be to tackle image hotlinking - another rampant bandwidth waste which happens even more often though wastes less bandwidth (at least in my case, simply because images are smaller in size than PDFs)
Thanks for your input!