DRM has become increasingly popular as a method to stop people playing a game without paying for it. Unfortunately some DRM is intrusive while others, such as this method is just plain funny.
If you have pirated Far Cry 4 on PC you may find that there is no Field Of View options and that the game is locked at a narrow FOV. Narrow FOVs in games can make some gamers experience motion sickness and a locked FOV is becoming increasingly unpopular amongst the PC gaming community. So, if you took to a forum to complain about the lack of FOV options then we would advise you remove those posts (if you can) because you have outed yourself as a pirate.
This is confirmed by Ubisoft Montreal's creative director Alex Hutchinson who said this on twitter
PC players! If you're online complaining about the lack of FOV control ... You pirated the game.— Alex Hutchinson (@BangBangClick) November 18, 2014
It may still be possible that you have bought the game and don't have an FOV slider because the option was introduced in a patch for the retail release. If this does apply then go online, update your game and enjoy. If this doesn't apply and you did pirate it... well... shame on you!