The fee was rumoured to be around the seven-figure range and Sa joins Reading having finished top scorer for Legia Warsaw with 14 goals in 26 games in Poland's top division.
Steve Clarke told the club's official website.
"The striking department was one area of the team that everyone agreed needed strengthening this season. Obviously Orlando's goal record is really impressive but, for me, I was most impressed by his answer to my question about why he wanted to come to play for Reading in the Championship. Immediately he replied 'I want to play in the Premier League again and Reading can take me there'. He is motivated to prove that his previous spell in England with Fulham came too early in his career. He is a strong player who leads the line well and has an eye for a goal. I'm sure he will be a big asset to the squad this season."
With Reading's strikers struggling in front of goal last season this is certainly a welcome signing for Royals fans who had grown restless with the club's lack of transfer activity after a disappointing season.
We'll have plenty more reaction and analysis to his signing on The Tilehurst End over the next few weeks.