Best way to "Reach the documents without alert any enemies" on Easy difficulty

There are 2 ways to complete this challenge in The Last Tiger, going through the front which involves sniping 4 soldiers with the Commando Carbine and going through the back which involves sneaking past one soldier and then stealthily taking down the two stationed in front of the rear door. Which way did you go and how should I take out the soldiers in each order?