Hi,
In the future, could you ask questions about AntFileConverter in the
AntFileConverter discussion group?
To answer you question, I think your raw files are not utf-8 encoded text files. Also, if you raw files are utf-8 encoded text files, there is no reason to convert the files, because you can use them as is.
I should also add that AntConc can read many different file types (including Word, PDF, and utf-8 encoded text files), so I suspect that you don't need to use AntFileConverter at all.
Laurence.