Have you run a couple of reg scanners rather than just ccleaner? Only when I did a major clear out of stuff recently I ran ccleaner and it found about a dozen orphaned reg entries, then I ran Uniblue's registry booster and it found about 220 orphaned entries. I feel it's got to be something in the registry that is triggered on opening a PDF using reader and it wont necessarily have 'Flaxmenu' in the entry.