For the past couple of months I've been getting this error: "this is not a valid Portable Document File (PDF) document. It cannot be opened." error when I'm NOT trying to open anything. I'd say it's happened maybe 10 times over the last couple of months and 9 of those times, it's happened when I'm waking the computer from sleep. I can't seem to figure out any pattern to it. It's like it's trying to open a file on it's own but it doesn't show in the recent list and I'm not seeing any action that could be doing this.