If you choose to not install importers during the CircuitStudio installation don't worry because you can add them later. To do so do the following:
1) Go to the CircuitStudio Start Page by going to View > Start.
2) Click on My Account and from the pull down menu select extensions and updates
3) Click on Configure on the right hand side
4) Check the boxes of the importers you'd like to use
5) You are now able to import by going to File > Import
I've added pictures to each of the steps below.
1) Go to the CircuitStudio Start Page by going to View > Start.
2) Click on My Account and from the pull down menu select extensions and updates
3) Click on Configure on the right hand side
4) Check the boxes of the importers you'd like to use
5) You are now able to import by going to File > Import