On an afternoon this spring, James Hirschfeld, a founder of Paperless Post, was at the company’s Lower Manhattan office surveying moodboards for digital invitation designs. They included materials for forthcoming motifs like New Victorian, a collection inspired by 19th-century décor, and a line by Annie Atkins, a graphic designer known for her collaborations with the director Wes Anderson.

As Mr. Hirschfeld examined the collagelike boards, he recalled a meeting about the design of new children’s invitations. “Someone said, ‘Dinosaurs are out, owls are in,’” he said. “And I thought, Is this my life?”

For the past 15 years, it has been.

Mr. Hirschfeld, 38, with his older sister, Alexa Hirschfeld, 40, started Paperless Post in 2009, when they were 23 and 25. He was a senior at Harvard and she was working at CBS as a second assistant to the anchor Katie Couric.

Since then the company has sent some 650 million invitations, according to its own metrics, has grown to employ a full-time staff of 110 people and, as of last year, has been immortalized in a “Saturday Night Live” sketch. Paperless Post has also earned fans in the heritage stationery businesses it sought to disrupt, collaborating with brands like Crane and Cheree Berry on digital products.

Its approach of combining the flourish of physical invitations with the ease of digital correspondence has been adopted by several younger companies, among them Electragram, a digital stationery business developed by the editor Graydon Carter and his wife, Anna Carter; HiNote, a similar business started by Alexis Traina, the wife of a former United States ambassador to Austria; and Partiful, a platform with a faster-and-looser sensibility that has resonated with members of Gen Z.

But when Paperless Post debuted, in certain corners of society its arrival was seen less as the dawn of a new era and more as a step toward the end of civilization as some knew it.

Pamela Fiori, an author who in 2009 was the editor of Town & Country magazine, told The New York Times back then that Paperless Post’s brand of digital stationery was representative of “a world increasingly uncivilized.” Ms. Fiori, now 80, said in an interview in April that although she still preferred using physical stationery, she could not deny the impact that the company has had in the years since it started.

“If you say Paperless Post now, people know immediately what you are talking about,” she said. “They do it well.”

Marcy Blum, a wedding and event planner in Manhattan who has worked with clients like the basketball player LeBron James and the interior designer Nate Berkus, was also among those who at first quickly wrote off Paperless Post.

“We thought, ‘This is convenient, but it isn’t going to change much,’” Ms. Blum said. “We were absolutely incorrect.” She added that her business had benefited from the service over the years because it allowed for planning more events at short notice.

“It’s like Kleenex now, right?” Ms. Blum said, referring to how the name Paperless Post has become a general term for digital correspondence in the same way Kleenex became a general term for tissues.

Heady Beginnings at Harvard

The Hirschfeld siblings began developing what would become Paperless Post in 2007. Mr. Hirschfeld had by then begun his sophomore year at Harvard after transferring from Brown, and was planning his 21st birthday party.

“Paper invitations were expensive and inefficient,” he said, adding that digital alternatives at the time like Facebook or the website Evite were “just unacceptable from a design perspective.”

Ms. Hirschfeld, who had graduated from Harvard, was living with their parents at the family’s home on the Upper East Side of Manhattan while starting her career in television. She had already begun to question that path, she said, when Mr. Hirschfeld called her with an idea to start an online business.

Neither had studied technology; Ms. Hirschfeld had majored in classics and modern Greek studies, and Mr. Hirschfeld was an English major. But they were motivated partly by what Mr. Hirschfeld described as a flourishing entrepreneurial spirit at Harvard in the wake of Mark Zuckerberg — a classmate of Ms. Hirschfeld’s — starting Facebook with his university roommates.

“That is what got my antennae out to start a company with Alexa,” Mr. Hirschfeld said. “I felt like it was possible because there were people around me there who showed me that.”

The siblings and their younger brother, Nico Hirschfeld, who is not involved in Paperless Post, also grew up in a family with entrepreneurs. Their maternal great-grandfather, Raphael Caviris, after coming to America from Greece, opened several diners with his brother including the Burger Heaven chain, now closed, in New York.

When they were teenagers, Mr. Hirschfeld was a waiter at Burger Heaven and Ms. Hirschfeld was a hostess. “We were used to being in and around small businesses,” he said.

The two siblings used personal savings to develop a prototype of their online business, which has always involved some combination of free offerings, to entice users, and paid premium services like customization. (These days, sending digital invitations with custom touches like special artwork and lined envelopes to 20 people can cost up to about $70.)

As the siblings began pitching the concept to investors in 2008, some balked at the notion that people would pay for digital invitations, no matter how nice they looked, Mr. Hirschfeld said. But they persuaded Ram Shriram, an early investor in Google; Mousse Partners, an investment firm for the Wertheimer family, which owns Chanel; and others to contribute almost $1 million to their fledgling venture.

“They took a chance on us,” Ms. Hirschfeld said. Mousse Partners even set the Hirschfelds up with their first work space: A spare row of cubicles at the New York office of Eres, the French lingerie and swimwear brand, which is owned by Chanel.

When the Hirschfelds started the business, it was called Paperless Press. But a web address with that name already existed and its owner would not sell it to the siblings, so within months they had switched to a new name: Paperless Post.

Guided by ‘Guts and Scrappiness’

Meg Hirschfeld, the Hirschfelds’ mother, attributed her children’s success partly to “guts and scrappiness,” qualities they inherited from their ancestors, she said. Mrs. Hirschfeld, who left a career as an attorney to raise her three children, is now the chief administrative officer at Paperless Post. Her husband, John Hirschfeld, is a real-estate investor.

She said Mr. and Ms. Hirschfeld were close siblings growing up, but had different sensibilities: He was creative and artistic, and she was outgoing and a computer whiz. Mrs. Hirschfeld recalled touring the Metropolitan Museum of Art with her son when he was in preschool, and her daughter becoming “absolutely hooked” on an Apple computer as a 7-year-old.

The siblings’ yin-yang brains are reflected in their duties at Paperless Post. Ms. Hirschfeld oversees the business’s operations and technological aspects. Mr. Hirschfeld is in charge of business development, marketing and design, a role in which he has tapped collaborators like the fashion brand Oscar de la Renta and the merchant John Derian.

The Hirschfelds, who each have a seat on Paperless Post’s seven-member board, are no less involved in running their business now than they were 15 years ago. But both described themselves as being less frenetic. Ms. Hirschfeld, who lives in the East Village, is a mother of two young children. Mr. Hirschfeld, who lives on the Upper East Side, also spends time on Long Island restoring a house from 1895 that he recently bought.

In recent years, their company has had to contend not only with newer competitors but also with the tumultuous economic climate caused by the pandemic. Mr. Hirschfeld described that period as “eye watering,” explaining that sales were down by between 50 and 80 percent in several months of 2020 compared with the same months in 2019. “Except in Florida and Texas,” he added, noting that the company shifted its marketing during that period to focus on places with less restrictive lockdown policies.

Changes in how people communicate — more texting, less emailing — have also posed challenges to Paperless Post’s business model.

“In 2009, it was just paper and email,” Mr. Hirschfeld said. “Now it is DM, WhatsApp.” As a result, the company has introduced products like Flyer, a casual, text-message-friendly form of invitation that is typically less expensive than Paperless Post’s traditional offerings.

Chloe Malle, 38, the editor of Vogue.com, was another skeptic of Paperless Post when it first debuted. “I loved print invitations,” said Ms. Malle, who was a classmate of Mr. Hirschfeld’s when he briefly attended Brown.

Then she started using the platform and, more recently, began receiving wedding invitations by email via Paperless Post. “That just wouldn’t have happened before,” she said. Now Ms. Malle is also receiving digital invitations through competitors like Partiful. But she thinks Paperless Post, much like print stationery, will always have its fans.

“There is room for both,” she said.