Open-source creator Anthony Stirling launches Stirling PDF to build the first open-core PDF editing suite

In January 2023, Anthony Stirling needed to do something seemingly simple—sign a PDF. He would soon find that to execute this simple task he would either need to pay someone money or use an untrusted third-party service. “My co-worker wanted me to sign a PDF but we couldn’t find a tool we trusted to use in our workspace,” Anthony explains. “Everything we could find was either paid or free but not open source.”

After turning to Reddit for help and coming up short, Anthony decided to create something himself. After a few ChatGPT prompts, Stirling PDF, a locally hosted web application designed for various PDF-related tasks, was born. “It initially started as an exploration of what I could do in a single day with ChatGPT—I have 24 hours, what can ChatGPT do?” said Anthony. “I came up with four features, posted it on Reddit, and it kind of blew up.”

After his original experiment, Anthony decided to ditch ChatGPT. Meanwhile, interest in Stirling PDF was growing fast and people were asking for more features. “After creating those first few features I said, ‘Okay, let’s never use ChatGPT again,’” said Anthony. “But it got so much following just from that, just because there was a gap in the market for an open-source app like this. So I just kept adding new features and improving it.”

Today, the open-source PDF editor has 50+ features, 6.2MM downloads on docker, and more than 150 people have contributed to the project. “The vast community interest in Stirling PDF combined with the speed at which it has developed makes the project particularly promising,” said Betty Ma, COO at OCV, “it embodies the power of open core companies.” Open source features like the ability to combine PDFs, Optical Character Recognition (OCR), and automated pipelines for PDF processing have generated much of Stirling PDF’s early usage.

With $2MM in funding, Anthony plans to add highly-requested enterprise capabilities. A recent survey of more than 6,000 users revealed that paid support, advanced form editing and filling, unique conversion types, and AI are top priorities. While nothing is set in stone, the long-term vision is to expand into other document formats. “I can see us starting Stirling Images, where it’s a similar layout to Stirling PDF but it’s for images,” said Anthony. “There are many ways we can use this same framework for different operations.”

Open-core PDF editing software

The PDF software market is “experiencing a significant surge,” according to a report by Global Growth Insights. The PDF software market is expected to grow between 11-18% from $3.35B to $15B over the next decade thanks to pandemic-era pressure to digitalize and the rise in remote work and learning. Security and compliance needs drive demand “as businesses seek reliable solutions to protect sensitive information and meet regulatory requirements” according to the report.

Self-hosted PDF applications are inherently more secure than SaaS apps making them the most popular choice—self-hosted apps are expected to account for 75% of the PDF software market by 2032. “It’s more secure when everything is local,” said Anthony. “No files leave your network. This is especially important for more regulated industries that handle sensitive data.”

While many proprietary self-hosted solutions exist, Stirling PDF is the only actively developed open-source web-based PDF editor. “Proprietary software requires users to place a high level of trust in a company,” said Sid Sijbrandij, General Partner at OCV. “With cyber security risks becoming more prevalent, today’s users want to be able to inspect the code and they want the option to control their data by self-hosting the software.”

Stirling PDF’s open-source feature set rivals closed-source and high-priced commercial solutions. “It started with merging and splitting PDFs, but now we have over 60 different operations,” said Anthony. Driven by community input and contributions, Stirling PDF’s feature-rich suite has achieved feature parity in under two years.

Better workflow automation and the implementation of AI are potential next developments for the suite. “We already have a function called ‘Pipelines’ where you can specify a set of operations and then run them automatically,” said Anthony. “With AI we hope to automate the creation of pipelines. Instead of manually creating the pipeline you just tell the AI bot what you want to do and it creates the pipeline for you.”

Partnering with OCV

Stirling PDF’s growth so far has been exponential with what started as a 24-hour challenge to solve a personal problem escalating into a popular and widely used open-source project. “It’s been quite a journey,” said Anthony. “Even at the start, I was surprised by how many people were using it and requesting changes. We even support over 30 languages now.”

With funding and support from OCV, Anthony is ready to harness the momentum and solve his next big challenge: build a commercial business. “Now I can dedicate real time to developing the features people have been asking for,” said Anthony. “Working with OCV comes with the added benefit of having a team to consult with and get insights on where to improve and what direction to take the software. It’s a huge benefit.”