Keep exploring the Centennial Building Library Area. Be sure to have the UV light is on so that you can spot any secret clues.  Check the shelves for books too, they will have clues, alas subtle, regarding the story. For example a book with an insert, "Nice Mr Neighbor illustrated by Thomas Stepanitz" showing a stranger luring a kid into a van. Make sure to grab the maps from the 2nd floor between rooms 207 and 208. Enter room 208 and exit it to the corridor behind. There is a painting of a girl on the wall "When you lose someone you love" There is an elevator in this walkway, but pressing the buttons has no effect. Keep going and enter another small room. In there you find a door with a number pad. This is a PUZZLE.

Library Keypad Solution
The numbers pad has buttons labeled from 1-9. You do not know the code yet. You will need to solve another puzzle to unlock this one,  or you can just cheat and scroll down to the solution.

Take the stairs down to the main area, note the display cases with the dolls inside. There is also a sign in one of the side rooms. Examine it to see that you are in the first floor, "Archive/Offices", and that at the top of the building is the radio station. There is a also a restroom at the end of the hall with a first aid kit inside. You will hear a voice eventually saying "Trust yourself Murphy. You know more than you think you do." As you explore the area with the glass cases, one of the doll breaks the glass and has her shadows attack you. You can either focus on the shadows or on the main doll itself. If fighting the shadow, make sure your UV flashlight is on, it will make the Shadow a lot easy to see. After dealing with it, go past a door near a fire hydrant, and enter another door to find yourself in a small office. There is another painting on the wall for you to examine, "Dangerous Beauty". Exit to a big hallway. There is another weird painting there, "Demon Samael".

Enter room 104. There is a body on the chair, grab an ID card from it. This is the Director's identification card. There is also a Colt gun on the table with the phone and the typewriter. If you point your forensic light at the wall, you can notice it says "Sequestered does not mean safe". Room 103 has some footsteps on the floor, revealed only by the ultra violet flashlight. They lead to a painting, "Devil's Pitstop". Examine rooms 102 and 101 as well. Room 101 has some pistol bullets on the sofa. From room 101 you can either explore room 100 or go back north to the main area with the display cases. There might be more attacks from dolls and shadows. Again, you can either attack the shadows and have the source doll take damage through that, or go straight for the source. If there is an easy access to the source mannequin then you should attack her directly. Otherwise, focus on the shadows.

Go to the west end of the floor, to office 105. This is the director's office. A radio plays the song "Nobody Knows the Trouble I've Seen" by Louis Armstrong. There is an card reader near the door. Use the ID card you obtained previously. Enter the office. On the desk there are some scattered envelopes. Murphy will remark that there is something written there. This is a PUZZLE

Envelope Puzzle Solution
There are papers with numbers spread on the desk. One envelope has "6" on it, another paper with the number "3",  one with two digits "85" and another one that says "11".  You can turn the envelopes left and right and also move them. Start piecing them together like a jigsaw puzzle. While the answer to this riddle is the same on all puzzle difficulties, the puzzle will start out differently based on difficulty:
Easy: Three of the envelopes fragments are in the correct spot, making this puzzle very simple to solve.
Normal: One of the numbered envelopes is in its right spot.
Hard: None of the envelopes are in position.

Notice that a portion of the desk is slightly lighter colored. This is from the dust, outlining where the envelopes stood originally. Use this outline to help you solve the puzzle. Here is what the solved puzzle looks like at the end:

Silent Hill: Downpour Office Envelopes Puzzle Solved

This gives you the keypad code, "851136". Enter this combination into the key pad to advance in the game.

Silent Hill Downpour Library Keypad opening code