Select the fading door tool in the tools list, and set a key (Doesn't matter what key you use) that will open the fading door.

Once you have set a key to open the fading door, close the menu and apply the tool (left click) on any props you want to be opened.

Back into the tools list, select the keypad tool (NOT the wire one!) and change the settings to how I have it.

After you have set the keypad's settings like I have (With your own password if you want), close the menu and add on 2 keypads (1 on inside of door, 1 on outside).

There are 3 ways to open a fading door with keypads, but 1 of them is for the owner of the door only.
1. Owner of door - hold down the key you set to open the fading door.
2. Putting in password - Put in the password you set by putting your crosshair over a button and pressing E. (Once password has been put in, press the "OK" button)
3. Hacking the keypad - Pull out a keypad cracker, get next to the keypad you want to open, and left click. During the hacking process, if you take your crosshair off of the keypad, you will lose all progress and will have to restart. This is the way to open keypads you don't own and don't know the password to.

If you have done everything how I have explained (And showed), then your door should open without a problem!

Thank you for reading =)