Programs enabling conversion of the file:
If your objective is to convert the file from AC3 to the file FLAC, you can use any of the applications listed. AC3 to FLAC conversion process in every program intended for this purpose (so-called converters) is very intuitive and everyone is able to manage converting a file.
However, bear in mind that the list may also include programs to support and work with the indicated extensions AC3 and FLAC - and not only converters. In such a case, you need to open the source file AC3 and from the options available in the program, choose ”Save as... FLAC" or "Export to FLAC".