Pop-up dictionary in Lion

I've got the pop-up dictionary working in Lion in both Safari and Email, but I can't get it to work in Preview, which is really the only place I need it. Can anyone confirm that this does indeed work in Preview by trying it on a document? I'd be pretty sad if this didn't work throughout Mac's main programs.

To try, just use three fingers to tap on a word in Safari or Mail (where I know it works). Then open a document in Preview and try it again. Just let me know if you get a pop-up. Or, alternately, you could press Control-Command-D while hovering over a word, then release to see the pop-up.

Thanks.

Why are you opening documents in Preview?
If they are .doc files, use MS Office for Mac if you have it, or these apps are free -> OpenOffice, LibreOffice, NeoOffice.
If they are RTF files, open them with Text Edit. Dictionary works in all these other apps I've mentioned.