Founded in Melbourne but now headquartered in San Francisco, Nitro competes with Adobe for a share in the PDF software market.
Its latest funding round attracted US$15 million from Battery Ventures, which previously invested in companies such as Akamai, Blue Jeans, Freescale, Groupon, Nutanix, Skullcandy and Splunk, as well as less well-known names.
Some Battery-backed companies have been acquired by top-tier enterprises such as Apple, Boeing, Cisco, IBM, Salesforce.com and Symantec.
The shopping list include more staff, particularly in Europe (founder and CEO Sam Chandler mentioned his hiring plans for Ireland in a recent interview with iTWire).
All told, Nitro expects to expand from 160 to 500 employees over the next three to five years.
The investment will also be used to build out Nitro's infrastructure.
Battery general partner Michael Brown will join the Nitro board.
"Every business deals with documents and knows the pain points in effectively sharing them and using them to collaborate with others. Both offline and online, Nitro is helping to solve these universal problems," he said.
"It's exciting to think that we've only just scratched the surface of this significant market opportunity and Battery is delighted to partner with the Nitro team to deliver on the company's vision of bringing smarter documents to everyone."
Nitro's first funding round was in 2012-13, when it raised $6.6 million from local investor Starfish Ventures.