A file can be processed through the effect chain in a similar way to the microphone data.
If you would like to preview how the file will sound once the voice has been applied, then you can use the Preview File button from the toolbar and then select the file you'd like to preview. While previewing the file, you can change the applied voice by using "Change Voice" button and selecting any voice desired. If you are happy with the results, use "Save As" to save processed file to a local folder.