Former Bills running back Karlos Williams has been conditionally reinstated by the NFL, according to Ian Rapoport of NFL.com (on Twitter). Williams has not played since his rookie year in 2015, but he may now have an opportunity to get his career back on track. 
The letter informed Williams of the good news and noted he was humbled and committed to not squandering his second chance. Provided that Williams stays clean following his substance abuse suspension, he should be able to sign with a club and suit up.
Williams averaged 5.6 yards per carry as a rookie (with nine all-purpose touchdowns) and showed serious promise. But, before the 2016 season, he was a surprise cut when he showed up to Buffalo out of shape. He later hooked on with the Steelers, but never played a down for Pittsburgh.
Eagles.