While I’m sure there are quite a few people out there who are able to plan far enough in advance to assign a shortcut to a macro while it is being created, I’m not in that club. I don’t usually think about creating a shortcut until I’ve used the macro several times and then decided that I wanted an easier way to execute it.
Fortunately, this isn’t a problem since Word 2007 allows you to go back and assign a shortcut to a macro after it’s been created. To do this, click on the Office button and select Word Options.

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Once the Word Options window opens, click on Customize. If you want to add a button shortcut to the Quick Access toolbar, select Macros from the Choose commands from drop down list, and perform the same steps as described in the preceding section for adding a button.

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If you would rather add a keyboard shortcut, click on the Customize button next to Keyboard shortcuts in this window.

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In the Customize Keyboard dialog box that appears, choose Macros from the Categories listing. Next, select the macro for which you would like to create a keyboard shortcut from the list of Macros.

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From here, the process of assigning a shortcut is the same as that described in the previous section.