Breaching Doors

Doors. Your worst enemy. The ones where security doesn't want you to go into are usually locked. Here is a list of them: You can't get too far in your mission without getting past doors. Luckily, all of these doors can be breached, either loudly or quietly. Here is how to do so!
 * Wooden locked doors
 * Metal locked doors
 * Key card locked doors

Method 1: Shoot it

 * Requirement: Suppressed Weapon
 * Process: Shoot the lock. Usually only two shots will break it.
 * Tips:
 * Don't shoot a door where many people will walk by. They can notice broken doors.
 * ONLY WORKS ON THESE TYPES OF DOORS!!!

Method 2: Unlock it

 * Requirements:
 * Lock Picks
 * Art of Steal
 * Process: Unlock the door.
 * Tips:
 * Make sure no one is watching you.
 * Take advantage of being able to close the door again.

Method 3: Drill it

 * Requirement: Silent Drill
 * Process: Drill the lock.
 * Tips:
 * If you are drilling a door in the open, make sure to have Precision Drilling.
 * It takes a long time. Overdrill may help.

Method 4: Blow it Up

 * Requirement: Breaching Charge
 * Process:
 * Apply Breaching Charge to the door
 * Hit 7
 * Tips:
 * Broken door = not closable. Choose doors wisely.
 * You probably shouldn't use the breaching charge on this door. There are much more cheaper alternatives...

Method 1: Unlock it

 * Requirements:
 * Lock Picks
 * Art of Steal
 * Process: Unlock the door.
 * Tips:
 * Make sure no one is watching you.
 * Take advantage of being able to close the door again.

Method 2: Drill it

 * Requirement: Silent Drill
 * Process: Drill the lock.
 * Tips:
 * If you are drilling a door in the open, make sure to have Precision Drilling.
 * It takes a long time. Overdrill may help.

Method 3: Burn it

 * Requirements:
 * Blowtorch
 * Firebug
 * Process: Burn the lock
 * Tips:
 * Sort of takes a long time. But at least it's silent!
 * You won't close the door after burning. Be careful!

Method 4: Blow it Up

 * Requirement: Breaching Charge
 * Process:
 * Apply Breaching Charge to the door
 * Hit 7
 * Tips:
 * Broken door = not closable. Choose doors wisely.
 * Silent drill with Precision Drilling is a good alternative.

Method 1: Unlock it

 * Requirements:
 * Key Card Scrambler
 * Prodigy
 * Process: Bypass the key card reader
 * Tips:
 * Make sure no body is watching.
 * Close the door if you will be entering restricted area.

Method 2: Unlock it (legally)

 * Requirement: Key Card
 * Process: Use the key card reader
 * Tips:
 * People won't get suspicious of you using the reader when watching you.
 * Usually providing access to restricted area, enter when no one is watching.

Method 3: Drill it

 * Requirement: Silent Drill
 * Process: Drill the lock.
 * Tips:
 * If you are drilling a door in the open, make sure to have Precision Drilling.
 * It takes a long time. Overdrill may help.

Method 4: Burn it

 * Requirements:
 * Blowtorch
 * Firebug
 * Process: Burn the lock
 * Tips:
 * Sort of takes a long time. But at least it's silent!
 * You won't close the door after burning. Be careful!

Method 5: Blow it Up

 * Requirement: Breaching Charge
 * Process:
 * Apply Breaching Charge to the door
 * Hit 7
 * Tips:
 * Broken door = still not closable. Keep choosing doors wisely.
 * Silent drill with Precision Drilling is still a good alternative.

Breaching Loudly
Luckily, breaching loudly can be used for almost every single door

Method 1: Blow it Up

 * Requirement:
 * C4
 * Demolitions Expert
 * Process:
 * Apply C4 to the door
 * Back away
 * Press 6
 * Tips:
 * C4s aren't only restricted to taking down doors. You can plant them anywhere and use them as mines against the SWAT that will be coming in soon.
 * Make sure you are standing back. You don't want to underestimate the range of the blast...

Method 2: Drill it

 * Requirement: Drill
 * Process: Drill the door
 * Tips:
 * This is insanely slow. You'd be better off using one of the stealth methods.
 * Every door is possible to breach. There is at least one way to break open a door in every mission.

Method 3: Stealth Methods

 * Requirement: Whatever you need for chosen method (see above)
 * Process: Whatever you need to do for said method (see above)
 * Tips:
 * Very limited, as many need different skills. Beware!
 * It's still faster than a drill, at least.

Wooden Doors

 * Requirement: A gun
 * Process: Shoot the door
 * Tips:
 * If there is a glass wall that leads into the room you're attempting to get in, go through that. Less ammo can be used.
 * Don't bother with other methods. This is the quickest with wooden doors.