BaseDecode

BaseDecode["string"] decodes the Base64 data contained in a string and returns the result as a byte array.

BaseDecode["string", "encoding"] decodes using the string using the specified encoding.

Examples

Decode Base64:

BaseDecode["SGVsbG8="]
(* ByteArray[{72, 101, 108, 108, 111}] *)

Please visit the official Wolfram Language Reference for more details.