Ctrl+D
- My OS is win7 Professional service pack 1
 - When i want to Duplicate a shape he short cut Ctrl+D won't apply, when they do work they undo which is not what i want.
 - I was expecting the function to duplicate the shape, but it didn't.
 - it either it undo or just won't do anything
 
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Ctrl + D in Illustrator does not duplicate. There is no such a command, unfortunately. Instead this hotkey does another useful operation by default, it repeats the last applied transformation again — like if you move something to the right, you can move it (or any other shape) again, with the same distance.
However, I agree that Duplicate command is something Ai might benefit from. Hitting Ctrl+C, Ctrl+F is still twice longer than one hotkey, and is nowhere instant, So please vote here for having it:
https://illustrator.uservoice.com/forums/333657/suggestions/44725447