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Strangely, I cannot make any hotkey work if I specify that item for Preview only, as suggested in comments. You can use the hierarchy syntax, as mentioned in Arthur Hammer's answer - Tools->Annotate->Highlight Text - but unless there is potential for confusion, if the same command was present in two hierarchies, performing slightly different tasks, for instance, then there is no need.
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Normally, you don't need to specify the menu hierarchy at all - simply use 'Highlight Text' as your menu item.
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The error is that you've partly listed the hierarchy, though incorrectly.
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