If the file isn't in the project (aka external), you can load it using the AJAX.RequestURL action. You will then be able to handle the response in a text format. Excel could then be hard to read, as the file isn't that much text-friendly. If it is a table you need, then try to use the CSV format instead.
Last thing, a warning : you have to store the requested file on the same domain as your application. AJAX won't be able to load something from another domain (this is a limitation from AJAX in all browsers : no cross-domain)