There is only one file type that uses the .NTH extension:
Nokia Series 40 Theme File
An NTH file contains a theme used for customizing the look and feel of a Nokia Series 40 mobile phone. It includes background images, icons, ringtones, and other custom options. NTH files are created using the Nokia Series 40 Theme Studio application.
NTH files are distributed in a compressed .ZIP format. Therefore, you can rename their extension to ".zip" and open them with any Zip decompression utility.
|Nokia Series 40 Theme Studio|
Updated: February 18, 2018