1. Drag and Drop below two Dlls to Unity assets
    a.Newtonsoft.Json.dll
    b.VisionworkplaceUnityLoader.dll
2. In Unity add "NewEmpty" gameobject. Create new c# script. Attach this script to EmptyGameobject. The script code should look like below to load any .unitydata file
-----------------------------------------------------------    
    using UnityEngine;
    using System.Collections;
    using System.Collections.Generic;
    // Step1: add visionworkplace name space
    using VisionworkplaceUnityLoader;

    public class LoadModelTest : MonoBehaviour
    {
        void Start()
        {
            //Step2: create UnityDataReader class object
            UnityDataReader modelHandler = new UnityDataReader();
            //Step3: The .unitydata may have views/cameras. So to get camera create views object.
            List views = new List();

            //Step3: call LoadGameObject method
            /*
            Call LoadGameObject()
            argument 1: List - this will be passed as reference to retrieve camera/views from .unitydata file
            argument 2: string .unitydata file path
            */
            GameObject go = modelHandler.LoadGameObject(ref views, "D:\\Technical_school-current_m\\Technical_school-current_m.unitydata");
        }

        void Update()
        {
            
        }
    }
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For more information on how external dlls can be used in Unity, follow this link
https://docs.unity3d.com/Manual/UsingDLL.html