The issue with .PDF is due to acrobat reader not supporting 64bit for the explorer extension that renders the preview image. I have seen workarounds where use of a 32bit explorer may solve the issue, but I'm not that worried to start hacking at explorer.
A related issue may be seen with certain applications that add a context menu item, (open with ..... Etc), the context menu entry does not work in x64. I know that 7Zip has this issue.
I have looked at various alternative readers but none I can find at the moment cure this issue, (although several are better readers than Adobe's
I have come to a compromise where I need to visually inspect my library of PDF's - I open he preview pane and this, (using a Foxit renderer), gives me all the detail I need until a suitable 64 bit reader comes along, (maybe Reader 10+)