HITMAN 2

As @SpudimusPrime89 said in a previous comment, this doesn't work in Hitman 2 as well due to a slight re-shuffle.

Now my tactic for his disguise is to pick up the 2 coins (no longer 3) on the box, throw a coin half way between you and Nolkfolk, let him get suspicious, and then you can run over, pick it up and then use the coin a 2nd time against the box with the start gear on, and then let him pick it up as you throw the final one into the "armory" which is to your left.
You can then subdue him and leave his body in there as nobody comes this way.

For the rest you can follow @Maka91 guide above, although I would personally use the helicopter extraction as it's quicker, also you don't have to follow Ritter once you have spoken to him and he will make his own way to the office if you want to go prep traps- but you do have to be in the room before he gets there.

Also, once you have this achievement you can work towards the "kill someone with an explosive" achievement easily using this method too. Simply take the remote explosive at the start, do the exact same tactic to get to the office, but when he starts putting his password into the machine, walk behind him, drop the explosive (he usually turns around as you drop it) and detonate as you walk around the corner towards the side window (before he becomes "alert"). You can casually walk to the helicopter extraction with no issue.

The easiest way to do this is Garrote the mechanic, straight across from the garage is a door on the other side to the right is rat poison turn around go up the stairs & into the kitchen & Garrote the guy in there & take his chef disguise, right on the other side of the kitchen is the bar same floor go poison the glass at the bar but first make sure Mr. Norfolk is at the balcony to the right, he will go to the bar very soon so try to be quick after he's poisoned follow him to the bathroom he'll start puking you can either Garrote him or Drown him then take his disguise & talk to Kalvin Ritter follow him to his office & once the door shuts behind you Assassinate him & boom achievement.

Here is my Silent Assassin run of Freeform Training, eliminating Kalvin Ritter while dressed as Terry Norfolk.

Target: Kalvin Ritter

Starting Equipment: None but pick up the lock pick on the box in front of you after starting.

If you're just interested in quickly unlocking the achievement and the challenges or score arent important to you here,

What the other guides don't specify is that, to unlock this achievement, you don't even need to finish the level, or bother at all with the scoring system.

The only requirement to unlock this achievement is to kill Ritter while disguised as Norfolk, no matter if you kill other people, get spotted, hunted,...

So the straightforward-est way to unlock this achievement :
During Freefall Training
> Pick a coin on the table
> Throw the coin to make Norfolk come away from the guard
> Kill him, take his disguise
> Enter the yacht and proceed to get to Ritter
> Kill ritter. Either with a pistol shot or by snaping his neck or pushing him

Achievement unlocks here, you don't have to worry about escaping.

Now sure this won't get you a good score even if you finnish it, but this is meant as the fastest way to unlock the achievement without considerations for the game scoring system. Most achievements arent even related to the in-game challenges or score anyway so if you're purely achievement hunting here, this will be the fastest way. And in the case not, you'll have to reply each scenariis more than a handful of time to unlock all the escalations/challenges anyway.

Cheers.

You can follow the video guide below to not only unlock this achievement but also complete all 9 "Feats" challenges at the same time.
If you haven't finished this mission so far, this will also unlock the following achievement for you: