"He is on the verge of becoming a good, solid major-league pitcher," Cook said. "He has to gain better control. He is a little bit wild, but he has always had a very good arm. It's a matter of putting it together from the standpoint of control."
Reardon, 31, compiled 35 saves in 62 appearances last year and has averaged 29 saves over the last five years.
"We gave up a front-line reliever, but we helped our pitching and catching," Cook said at a news conference. "Without bolstering our starting pitching, a short man becomes somewhat of a luxury."
Reed, 24, is a lefthanded-hitting catcher who batted .236 with 2 homers and 9 RBIs in 68 games.
"We think he should be the backup behind Mike Fitzgerald, and he is capable of being first string," Cook said.
Perez and Cardwood will be assigned to the Expos' farm system but are big- league prospects, Cook said.
Perez, a 19-year-old lefthander, posted a 4-11 record with Class A Kenosha of the Midwest League. Cardwood, a 24-year-old righthander, went 11-6 with Visalia of the Class A California League.
Nieto, 26, batted .200 for Montreal last season in 30 games.