UTF-8: with BOM
UTF-8N: without BOM
Let's use nkf.
http://www.atmarkit.co.jp/ait/articles/1301/25/news092.html
Download to your local directory , set path to nkfwin\vc2005\win32(98,Me,NT,2000,XP,Vista,7)Windows-31J
Create sample file with note pad++ by using encoding UTF-8.
``
Open comand prompt,execute commmand
nkf32.exe -w test.txt > test2.txt