FileDragAndDrop.cs

using System.Collections.Generic;
using UnityEngine;
using System.Linq;
using B83.Win32;


public class FileDragAndDrop : MonoBehaviour
{
    // important to keep the instance alive while the hook is active.
    UnityDragAndDropHook hook;
    void OnEnable ()
    {
        // must be created on the main thread to get the right thread id.
        hook = new UnityDragAndDropHook();
        hook.InstallHook();
        hook.OnDroppedFiles += OnFiles;
    }
    void OnDisable()
    {
        hook.UninstallHook();
    }

    void OnFiles(List<string> aFiles, POINT aPos)
    {
        // do something with the dropped file names. aPos will contain the 
        // mouse position within the window where the files has been dropped.
        Debug.Log("Dropped "+aFiles.Count+" files at: " + aPos + "\n"+
            aFiles.Aggregate((a, b) => a + "\n" + b));
    }
}