The Encoding and Decoding commands are found under the Tools menu.
There are commands to encode or decode all the selected files into/from BASE64 format.
Encoding a file into base64 format is done if you want to convert a binary file into a format that is text-friendly. Base64 encoded files grow about 25-50% in size compared to their binary format.
Decoding a base64 file will turn the file back into its original form.
Read more about base64 at wikipedia here.