Each door in the RDT file follows this layout in the hexadecimal code:

3B NN 01 31 ?? 00 XX XX YY YY ZZ ZZ RR RR NX NX NY NY NZ NZ NR NR ST RN CA ?? DR DO ?? LF KK ??

3B = always the same in every door code. (Don't change it)
NN = the door number, 00 is the 1st door, 01 the 2nd etc. just make some changes to a door link to find out which door it actually links to if the linked room has multiple doors.
01 = always the same in every door code. (Don't change it)
31 = always the same in every door code. (Don't change it)
?? is unknown, no clue what it does, so leave it alone...
00 = always the same in every door code. (Don't change it)
XX = X co-ords (Co-ords go Low High).
YY = Y co-ords
ZZ = Z co-ords
RR = Rotation ?? (those two seemed to affect the Door position but not the NextRoom Position.
NX = Next Room Start X co-ords (doors have an access width as to why each co-ord has 2, a beginning and an end).
NY = Next Room Start Y co-ords (This is normally 0000)
NZ = Next Room Start Z co-ords
NR = Next Room Rotation
ST = Stage (for example Kendo's shop is Stage 0 Room 1 so it would appear as 0001)
RN = Room Number
CA = Camera Angle of next room (I.E. Where the Camera is).
?? is unknown, no clue what it does, so leave it alone...
DR = Door type. Wooden, metal, Stairs, lift. (Remember there is an UP/Down,In/Out version of Doors/Stairs/Lifts etc.)
DO = Door Open.
?? is unknown, no clue what it does, so leave it alone...
LF = Locked Flag (If I set another door to the same Hex as a locked door, it too becomes locked but if either door is opened the other becomes unlocked.)
KK = Key Needed
?? is unknown, no clue what it does, so leave it alone...

Values for DR:
00 = Wooden 4 Rectangle Door (Handle Left) (Opens away from Player)
01 = Wooden 3 rectangle door (Handle left) (Opens away from Player)
02 = Wooden 4 rectangle door Blue (Handle left) (Opens away from Player)
03 = Wooden Rectangle with Diamonds door (Handle left) (Opens away from Player)
04 = Wooden 6 Rectangle Blue (Handle left) (Opens away from Player)
05 = Wooden 3 Rectangle (Handle left) (Opens away from Player)
06 = Metal Door X (Handle Left) (Opens away from Player)
07 = Metal Door Plain with small grill at bottom.(Handle left) (Opens away from Player)
08 = Metal Door 2 Rectangles (Handle left) (Opens away from Player)
09 = Wooden Door 6 Rectangles (Handle left) (Opens away from Player)
0a = Gate with Bars (Handle left) (Opens away from Player)
0B = 2 Windows 4 Diamonds (Handle left) (Opens away from Player)
0C = RPD Doors (open towards Player) (Opens away from Player)
0D = Wooden 3 rectangle door (Silver Handle left) (Opens away from Player)
0E = Metal Stairs Up
0f = Wooden Stairs (1F West Stairs)
10 = Lift Gate (Open Right to Left)
11 = Double wooden door. Metal Grill at bottom, right door opens away from player.
12 = Stone Basement Steps. Up
13 = Grey Metal Door. Big window (with XXX)
14 = Double Width Metal Door. Slides Right to Left (handle on Right)
15 = Metal Door 2 X, 1 High, 1 Low, Black/Yellow /// in centre.
16 = Metal Ladders
17 = Old Ring Handle Door Left opens away from player
18 = Green Wooden Door Gold Handle Left Opens away from player
19 = Metal Circle Handle Left Lab Door. Slides Left to Right.
1a = Metal Door 3 Rectangles Handle Left Opens away from player
1b = Autopsy Double Doors, Opens towards player.
1c = Metal Door. Knob (left). Grill at bottom. Barred Window
1D = Metal Door Brown. Grill at top.
1E = Air Vent
1F = Metal Door Opens Up/Down by Splitting. Sewer X-DR
20 = No Door Ada Scream.
21 = No Door Birkin Sounds
22 = Brown Rusty Metal Door Handle Left Opens away from player
23 = Grey Metal Door with Border (sorta B ) Handle Left Opens away from player
24 = Grey/Green Metal Door, Metal Foot Guard, Window Handle Left Opens away from player
25 = Shaft Type L Automatic Door.
26 = Brown Metal Doors with twist Handle Left. Left Door opens Away From Player
27 = Double Teethed Metal Doors. Doors Slide apart.
28 = Red Small Elevator Up
29 = Shaft Type M metal Door, Handle Left Opens away From Player
2A = Metal Slide Left to Right Door. Small Window Up, Small Grill Bottom.
2b = Dumping Area B2 Shutter.
2c = Black/Red Sliding Doors with small windows.
2D = Scenario 1 End Lift Up
2e = Metal Door Bars, Handle Left Opens AFP RED Green light Above handle
2f = Turquoise Inverview Room Door. HL AFP
30 = Bus Double Doors open AFP
31 = Frozen Type-P Double Metal Door. Left Door opens AFP
32 = Please Wait Clothes Change.
33 = Vent
34 = Side Pack is being equipped.
35 = Vent
36 = Black Screen. *Drip Drip*

Values for DO:
0 = Handle Left, open Away From Player Lifts/Stairs/Ladders Up
1= Handle Right towards player. Lifts/Stairs/Ladders Down.
Some rooms use above 1 for the Door open but most doors end up with a blank screen if you do.