The 21-year old New Zealand international has completed his much-talked about shift to Europe after a fine season in Australia which landed him the A-League Player of the Year (Johnny Warren Medal) and Young Player of the Year awards.
"Marco has just been voted player of the year in Australia but that's not the only reason we noticed him,'' Bobic told the club's official website.
"He is a player who is well used to the attacking wide positions and provides speed. It will be interesting to see how quickly he can get used to the pace in Germany.''
Rojas added that he was determined to adjust to German football as quickly as possible.
"It's important to continue to push myself, to become a better player and it's important to be playing games. That's probably the most important thing," Rojas said.
"No matter how hard you train and how much you do during and after training, it's always important to be playing the games and being in the match situations, that helps more than anything."