public partial class Form1 : Form
    {
        Guid instanceId;

        public Form1()
        {
            List<int> list = new List<int>();
            list.Add(123);
            list.Add(123);

            InitializeComponent();
            dataGridView1.DataSource = list;

            DataGridViewLinkColumn lnk1 = new DataGridViewLinkColumn();
            dataGridView1.Columns.Add(lnk1);
            lnk1.Name = "pdf";
            lnk1.TrackVisitedState = false;
            lnk1.HeaderText = "Файл PDF";
            lnk1.Width = 80;

            foreach (DataGridViewRow row in dataGridView1.Rows)
            {
                row.Cells[dataGridView1.Columns["pdf"].Index].Value = "test1";
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            foreach (DataGridViewRow row in dataGridView1.Rows)
            {
                row.Cells[dataGridView1.Columns["pdf"].Index].Value = "test2";
            }
        }


        private void Form1_Load(object sender, EventArgs e)
        {
            foreach (DataGridViewRow row in dataGridView1.Rows)
            {
                row.Cells[dataGridView1.Columns["pdf"].Index].Value = "test0";
            }
        }



        private void dataGridView1_CellValueChanged(object sender, DataGridViewCellEventArgs e)
        {
            if (e.RowIndex < 0) return;
            object obj =
                dataGridView1.Rows[e.RowIndex].Cells[e.ColumnIndex].Value;
            if(obj!=null)
                Console.WriteLine(23);
            this.Text = obj==null? "NULL": obj.ToString();
        }
    }