DraggableForm.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Instagram
{
    public class DraggableForm : Form
    {
        private const int WM_NCLBUTTONDOWN = 0xA1;
        private const int HT_CAPTION = 0x2;

        [DllImportAttribute("user32.dll")]
        private static extern int SendMessage(IntPtr hWnd, int Msg, int wParam, int lParam);

        [DllImportAttribute("user32.dll")]
        private static extern bool ReleaseCapture();

        protected override void OnMouseDown(MouseEventArgs e)
        {
            base.OnMouseDown(e);
            if (e.Button == MouseButtons.Left)
            {
                ReleaseCapture();
                SendMessage(Handle, WM_NCLBUTTONDOWN, HT_CAPTION, 0);
            }
        }
    }
}