The team announced the deal Thursday, a day before the start of Oakland's rookie minicamp.
The Raiders drafted Cooper fourth overall out of Alabama last week to give quarterback Derek Carr the big-play receiving option he lacked last season.
Cooper is the career receiving leader at Alabama with 228 catches, 3,463 yards receiving and 31 touchdown catches. He led the nation with 124 catches last season in the tough SEC and ranked second with 1,727 yards receiving and 16 touchdown catches
The Raiders also announced the signing of undrafted rookie receiver Josh Harper, who was Carr's teammate at Fresno State.
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