Five-time Ballon d'Or winner Ronaldo swapped three-time reigning European champions Real Madrid for Juve in a sensational deal that will cost €100m (£88m/$117m) plus €12m (£10.5m/$14m) in additional charges.
The 33-year-old – Madrid's all-time leading goalscorer – signed a four-year contract with the Serie A giants.
Asked about new team-mate Ronaldo, Pjanic told Sky Sport Italia: "He's a huge coup, a great player."
However, Pjanic's future in Turin is far from certain, with new Chelsea boss Maurizio Sarri reportedly looking to lure the Bosnia-Herzegovina international to Stamford Bridge.
Pjanic – who arrived from Roma in 2016 – has now emerged as a possible target for Chelsea as Sarri seeks another central midfielder in London.
As he left a restaurant on Wednesday, Pjanic was quizzed on his future with Juve and the 28-year-old replied, "have a good evening" before driving away in his car.
Juve have already signed Ronaldo, Joao Cancelo, Emre Can and Mattia Perin, while Manchester United star Paul Pogba has been linked with an unlikely return to the club as well.