At the start of Episode 6, you and Sarah will enter room 943. After looking around for a minute, the room will go crazy and all the lights will go out. You need to close your eyes to see the ghost pointing at a piece of paper on the wall. Look at the paper with your flashlight and then close your eyes again to see the ghost pointing at something else. Continue this pattern to spell out a message from Theophile. This triggers another cutscene where you speak to Theophile’s ghost, unlocking the achievement.