What's wrong with this script?

What exactly does this script do? And in unity it gives me an error that says "Assets/DoFAutoFocus.cs(29,17): error CS0246: The type or namespace name `DepthOfField' could not be found. Are you missing a using directive or an assembly reference?"

I got it from here.

 using UnityEngine;
 using System.Collections;
 using System;
  
 /// <summary>
 /// PlayFM
 /// DoFAutofocus.cs
 /// 
 /// HIGH Quality checks every Frame
 /// NORMAL Quality in Fixed Update
 /// 
 /// BMBF Researchproject
 /// PlayFM - Serious Games für den IT-gestützten Wissenstransfer im Facility Management 
 ///    Gefördert durch das bmb+f - Programm Forschung an Fachhochschulen profUntFH
 /// http://playFM.htw-berlin.de
 ///    
 ///    <author>Frank.Otto@htw-berlin.de</author>
 ///
 /// </summary>
  
  
 [RequireComponent(typeof(Camera))]
 [RequireComponent(typeof(DepthOfField))]
 public class DoFAutoFocus : MonoBehaviour
 {
  
     private GameObject doFFocusTarget;
     private Vector3 lastDoFPoint;
     private DepthOfField dofComponent;
  
     public DoFAFocusQuality focusQuality = DoFAutoFocus.DoFAFocusQuality.NORMAL;
     public LayerMask hitLayer = 1;
     public float maxDistance = 100.0f;
     public bool interpolateFocus = false;
     public float interpolationTime = 0.7f;
  
     public enum DoFAFocusQuality
     {
         NORMAL,
         HIGH
     }
  
     /// <summary>
     /// Init all needed objects
     /// </summary>
     void Start ()
     {
         doFFocusTarget = new GameObject ("DoFFocusTarget");
         dofComponent = gameObject.GetComponent<DepthOfField> ();
         dofComponent.objectFocus = doFFocusTarget.transform;
     }
     /// <summary>
     /// 
     /// </summary>
     void Update ()
     {
  
         // switch between Modes Test Focus every Frame
         if (focusQuality == DoFAutoFocus.DoFAFocusQuality.HIGH) {
             Focus ();
         }
  
     }
  
     void FixedUpdate ()
     {
         // switch between modes Test Focus like the Physicsupdate
         if (focusQuality == DoFAutoFocus.DoFAFocusQuality.NORMAL) {
             Focus ();
         }
     }
  
  
     /// <summary>
     /// Interpolate DoF Target
     /// </summary>
     /// <param name="targetPosition">
     /// A <see cref="Vector3"/>
     /// </param>
     /// <returns>
     /// A <see cref="IEnumerator"/>
     /// </returns>    
     IEnumerator InterpolateFocus (Vector3 targetPosition)
     {
  
         Vector3 start = this.doFFocusTarget.transform.position;
         Vector3 end = targetPosition;
         float dTime = 0;
  
         Debug.DrawLine (start, end,Color.green);
  
         while (dTime < 1) {
             yield return null;
             //new WaitForEndOfFrame();
             dTime += Time.deltaTime / this.interpolationTime;
             this.doFFocusTarget.transform.position = Vector3.Lerp (start, end, dTime);
         }
         this.doFFocusTarget.transform.position = end;
     }
  
     /// <summary>
     /// Raycasts the focus point
     /// </summary>
     void Focus ()
     {
         // our ray
         Ray ray = camera.ScreenPointToRay (Input.mousePosition);
         RaycastHit hit;
         if (Physics.Raycast (ray, out hit, this.maxDistance, this.hitLayer)) {
             Debug.DrawLine (ray.origin, hit.point);
  
             // do we have a new point?                    
             if (this.lastDoFPoint == hit.point) {
                 return;
                 // No, do nothing
             } else if (this.interpolateFocus) { // Do we interpolate from last point to the new Focus Point ?
                 // stop the Coroutine
                 StopCoroutine ("InterpolateFocus");
                 // start new Coroutine
                 StartCoroutine (InterpolateFocus (hit.point));
  
             } else {
                 this.doFFocusTarget.transform.position = hit.point;
             }
             // asign the last hit
             this.lastDoFPoint = hit.point;
         }
     }
  
 }