Notable was founded by three 20-something Auckland University students, Hengji Wang, Alliv Samson and Jordan Thoms, who remain the major shareholders.
They were finalists in the university's annual Spark Challenge in 2012 and set up the company the following year.
Growth has accelerated in the past year since the company pivoted the app from just being aimed at students taking notes to all users.
It has had over 500,000 users and 1 million downloads since March 2014 and is now the leading PDF viewer app on the Google web store.
The start-up is chasing both the education and professional sectors and will use the additional funds to build more business partnerships, particularly in North America, and on product development and hiring more staff.
Some 80 per cent of users are US-based and chairman Bob Drummond said that follows a decision last year in the US for K12 schools to use Google Chromebooks, for which there are a limited range of apps, as the standard technology.
"There's enormous potential for growth in the US with a lot of schools and enterprises that have not been involved yet.
Both market segments are growing at a parallel quantum rate," he said.
The start-up's focus is on growth rather than profitability at this stage, Drummond said.
Users can download the app for free or pay for premium versions that add on more tools, and there is special pricing for school users.
Drummond said no sales have been made to schools in New Zealand yet.
The founders have been attending a number of education conferences in the US including one in Orlando, Florida, in January where Notable's freebie handouts included Whittaker's chocolate.
