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how can I enable in the three fingers gesture that shows the selected word in the dictionary?

This gesture works great in but doesn't in

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Strange enough, even the shortcut for it does not work. – Ivan Z. Xiao Sep 12 '11 at 15:45

Are you viewing a PDF? Unfortunately, the three finger tap gesture does not work with PDF files across the system (e.g. not in Safari as well).

The most convenient alternative I can think of is double tapping a word to select it and then two-finger tapping on that word to show the context menu in which you find the command "Look up word in dictionary".

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May I ask how you know it does not work with PDF? Is it said in the official document? I checked and seems true. But I just cannot imagine why it does not work, since literally you have the "Look up word" option. – Ivan Z. Xiao Sep 12 '11 at 15:45
It's just a guess from my side, judging from the behavior I observed. And with the technical background knowledge that different programming elements are used in OS X to display normal, editable text and to display PDFs. My guess is that it wasn't deemed important to make the latter behave as the former in that respect. – mss Oct 7 '11 at 20:17
Okay, after some observation I found that sometimes it works while sometimes not. Have no idea what is going on. – Ivan Z. Xiao Mar 6 '12 at 3:30

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