"It's a terrific fit for us, and the investors, as well," said Lee. "It's an excellent way to fund the growth of the company."
NextPage was started in 1999 when it created products for Internet searches. That business was sold, and the company then began work on its document management system.
The company includes leading professional services companies among its clients and also in the areas of accounting, energy, banking and insurance, Lee said.
NextPage was named a "Cool Vendor" in content management in 2011 by Gartner Inc., a technology research company.
Proofpoint offers security and management of sensitive data. Its products are delivered through the Internet, like most of NextPage's, a business model known as software as a service.
Lee said he will remain at NextPage and report to Proofpoint CEO Gary Steele, whom he met a few years ago. When Proofpoint wanted to open an office in Utah, Lee convinced Steele to share part of the same Draper building where NextPage is housed.
The combined companies have about 50 employees in Utah and are hiring engineers and salespeople.
"Utah will be a pretty significant and growing location for us," he said. "They're actually moving some of their product here and, of course, we're going to add on to the NextPage team to expand it, as well."
Proofpoint's filing with the Securities and Exchange Commission says its revenue grew from $31.1 million in 2008 to $52.5 million last year, but it had a net loss every year, including $13.7 million in 2011.