asCharBuffer() is not what you want here - unless the character encoding happens to be UTF-16, maybe. You need to know what character encoding the files uses, and use that encoding to translate from bytes to chars. Something like this:
I assumed UTF-8 for encoding; replace as apprpriate. If you're not sure what the encoding is, just try some common ones: UTF-8, ISO-8859-1, Cp-1252, UTF-16. (You won't notice a difference between the first three unless you use some non-US-ASCII chars like é or ™ - those sorts of things are represented differently in different systems.