Inside the office/storage room, there is a switch on the wall that turns on a purple UV light.
Are you having trouble finding the or navigating the spider tunnels to get to the lockers? Penumbra Overture | The Blank Paper | #10 Penumbra Overture
The paper is hidden inside one of the lockers. How to Reveal the Secret Text Inside the office/storage room, there is a switch
Open your inventory, select the "Blank Note," and use it while standing under the UV light. Inside the office/storage room