Nitro, a San Francisco-based provider of document productivity and workflow solutions, told peHUB that it has raised $6.5 million to date. Nitro, which announced product news earlier this week. raised a $3.5 million round in early 2012 and a previously unannounced $3 million round that the company secured in May. Australian-based Starfish Ventures was the sole investor in both rounds. Anthony Glenning, an investment director at Starfish, is the firm’s representative on the Nitro board.