var builder = new OleDbConnectionStringBuilder
{
    Provider = "Microsoft.ACE.OLEDB.12.0",
    DataSource = "D:\\db.accdb",
};

using (var connection = new OleDbConnection(builder.ToString()))
using (var command = new OleDbCommand("INSERT INTO Images (Img) VALUES (?)", connection))
{
    var bytes = File.ReadAllBytes("D:\\File.pdf");
    command.Parameters.Add(
        new OleDbParameter("@Img", OleDbType.LongVarBinary, bytes.Length, ParameterDirection.Input, false, 0, 0, null, DataRowVersion.Current, bytes)
    );
    connection.Open();
    command.ExecuteNonQuery();
}