I have enough problems focusing on what I'm reading without additional distractions. Just the flashing ad at the top of this screen made me have to refocus on what I was writing.
There's an ad flashing on this page? Hmm, guess Adblock for Firefox and SafariBlock for Safari are preventing me from seeing that.
As to ads in pdfs, nope, definitely do not want that. Though if they go ahead with this, there will probably be a tool created to strip the ads out arriving shortly afterwards.