how can i insert files into access database (in desktop application)

All you have to do is read the file into a byte stream

byte[] data = File.ReadAllBytes(path);

then use a parametrized query to insert it to the database. I would recommend you use a OleObject field type as otherwise you may find yourself out of space.

using (OleDbConnection con = new OleDbConnection(strConnect))
    {
    con.Open();
    using (OleDbCommand com = new OleDbCommand("INSERT INTO myTable (myFile) VALUES (@FILE)", con))
        {
        com.Parameters.AddWithValue("@FILE", data);
        com.ExecuteNonQuery();
        }
    }