Reds signed goalkeeper on a 28-day loan from League Two rivals Portsmouth on February 1, 2016 for his second spell with the club.
Paul was a popular figure at Reds after signing in May 2012. He was an ever present for the next two seasons in League One, making 105 league and cup appearances for the club.
He then joined Portsmouth in 2014 and has made 45 appearances for the Fratton Park club.
The 29-year-old, who started his career at Leyton Orient and also played for Exeter City and Peterborough is closing in on 400 career games.