The Far Cry 4 Tread Lightly Trophy / Achievement will give you one Bronze Trophy or 20 Gamerscore points. You need to play on an Outpost without triggering an alarm. It is possible to get this Trophy / Achievement in any mode.
First of all look for an Outpost and disable it by pressing Square (PlayStation) / X (Xbox), there are 24 Outposts in Far Cry 4 to choose from. Once you have disabled an Outpost get rid of all the enemies present.
It is alright if you are seen, you need to take care that they do not raise an alarm. In case an alarm is raised, commit a suicide, (don't be a fool, we are talking about the game here!) You will respawn near the Outpost and start over. Pick easy Outposts and if you have liberated all Outposts you can reset them in the game options under "Gameplay Campaign."
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