Dowtin entered the NFL with the New York Jets last season as an undrafted free agent out of North Alabama. He appeared in three games for the Jets after being elevated from the practice squad on Oct. 17.
Dowtin was signed to a reserve-future contract with Philadelphia on Dec. 31 of last year. He was released by the Eagles on April 11.
The Bills went 6-10 last season, allowing 435 points.