Jump they say - Reach the Animus memo
This achievement is unmissable and pertains to the story progression
As you progress through memory 3 of the Lost Archive DLC, you will come to a room with a large cube in the center and an abyss below. Once you solve the puzzle of this room, which is actually quite simple and merely requires a bit of timing and quick movement, you will pass through an animus gate where you will unlock a new block to place. Face forward and switch to the new block (it's a very distinctive Greenish/blue flat square block) and place one in front of you, step forward, and sproing (that means jump..) into the hole far in front of you. You will see an envelope floating directly in your path. Grab it and you'll snag this achievement.
Hope this helps, leave any comments to help make this a better solution!