Raven door code help?

You aren't going to be able to until later after the Tower of London mission. After that, you can find the four digits spread out across the bunker. One is in the mirror by the door, for the others, you can find a trail (presumably of blood) when scanning the room with your blacklight. Just follow the trails and they'll lead you to the other three numbers.

Once you do the Tower of London quest, you get the ability to read the Enochian language. At that point, return to the warehouse. Clear out the area around the keypad, then go into the room BESIDE the keypad room (Not the huge warehouse room, the office room). If you look through the glass towards the keypad, you'll see that the Raven of Dee above the keypad door is incomplete. In addition, some pain marks that look like they can be the missing stuff is on the glass. Move around so that they line up, then scan it. You should get the code then.

To be able to get the code, you need to make sure that the Raven of Dee symbol is complete. You can scan it once you got the wings, body, and the letters/numbers.