The file extensions in your subject line represent different ways digital books are packaged:
You will almost never find a commercial LIT file today. If you have a LIT copy of this novel, it is likely an older DRM-free scan from the early 2000s. To read it on modern devices, use Calibre (free software) to convert LIT → EPUB or MOBI. The Dark Fields by Alan Glynn aka Limitless EPUB.LIT. MOBI