i've been getting pissed off by this intrusive "Did you know..." box on my screen when I open a PDF in my Firefox browser (with Windows 7), so I came here looking for a solution. Was very disappointed by Evernote's handling of this, but encouraged by RAYD's remarks, so I tried clicking on the webclipper "elephant face" small icon (up in my browser's control lines, for feature/functions links), and it opens up with an "options" setting at the bottom, that will take you to a checkbox next to "Show save to Evernote button on PDF pages", which I unchecked and SAVE'd. After a limited amount of browsing to other PDF's, it seems to be working (that is, NO F'ing Pop-up box !) It's webclipper V 6.10.2, also. I hope like hell that this prevents this box from popping up again in the future, but it may be limited, like someone else said, to only working if you're logged in to Evernote while you're browsing. BTW, I'm NOT a paying customer, I'm a free version user.
Note to Evernote, you really don't deserve any applause for your denial of customer satisfaction or general inability to inform people here on this particular discussion of how to make your product run satisfactorily. It's been pathetic to read through ALL these notes, to find squat from you ! Why bother hosting a moderated customer forum if you're not going to have an informed, customer-friendly support person monitoring it and improving your customers' satisfaction ? Glad I'm not actually paying you anything ! I hope that this "turn off the Show Save" button continues to work after I close & open my browser, because I've been getting REAL SICK AND TIRED OF YOUR POP-UP.