You can do this from the symbol selector. To access the symbol selector, either hit the 'S' button on your keyboard, or from under the Charts menu select 'Change Symbol'.
In the lower-right corner is a button called hard drive. Please note that you will not have access to this button if you are using the Silver version of the software. Clicking on this button will produce the following window:
You can then navigate on your hard drive to where the data files are located. Keep in mind that they must be in either CSI or Metastock format.
You can view the data and add indicators or drawing objects. The main limitation is that you cannot run mechanical strategies on imported data.