Open-source alternatives to Adobe Acrobat

Most people in most offices don't need Acrobat. They need to stick three PDFs together, take a page out, fill in a form or knock a file size down so it will go by email. Acrobat Pro for teams is £20.22 a person a month on an annual plan, so five people pay about £1,213 a year for that.

The free alternative is usually one of those PDF websites, which means uploading your contracts to a company you've never heard of. The tools below do those everyday jobs without that. One thing has changed, though, and it matters: the name most people recommend here, Stirling PDF, isn't the fully open project it used to be.

BentoPDF

BentoPDF is a toolkit that runs in your browser, with over 100 PDF tools. You host it once and everyone in the office goes to the same address.

• Files stay on the computer. All the processing happens in the browser, and the project says files are never uploaded to a server. That's a neat answer to the "where did my contract go?" question.
• The everyday jobs. Merge, split, reorder, rotate, compress, add page numbers and watermarks.
• The harder jobs. Edit existing text, redact content for good, build fillable forms, compare two PDFs, and convert to and from PDF.
• Digital signatures using X.509 certificates, with the private key staying in the browser.
• Light to run. It's a static web app, served from one Docker container or any web server.

Two things to know. By default, some processing engines load from a public CDN when needed. Your documents don't go with them, but if you want no outside calls at all, the project provides an air-gapped setup. And the signing feature may need a proxy, which the README describes as required.

The licence needs a sentence of its own. It's AGPL-3.0, a proper open-source licence. BentoPDF also sells a $79 commercial licence, and its licensing page says an internal tool whose source isn't shared with its users needs one. My reading is that an unmodified copy, with the public source a link away, sits fine under the AGPL. If you've changed it and don't want to share those changes with your users, buy the licence. At $79 once, I wouldn't lose sleep over it.

PDFsam Basic

PDFsam Basic is the plain, reliable option. It's a desktop app for Windows, Mac and Linux that merges, splits, rotates, mixes and extracts pages.

There's no server to run. It works offline, adds no watermarks and has no file size limits. If those few jobs are all that you use Acrobat for, install this and you're done.

It isn't an editor, though. For text changes, forms or signatures you'll need something else. The company's site offers paid products for that, and only the Basic version is covered here.

Stirling PDF

Stirling PDF is the big name, with over 95,000 stars on GitHub. It offers 50+ tools, runs on your own server, and has a REST API and no-code automation, so it can do jobs that a browser-only tool can't, such as processing files from your other systems.

But it needs an honest label. The project now calls itself open core. Its licence keeps MIT for part of the code, while several folders, including engine and app/proprietary, sit under a Stirling user licence that requires a paid subscription for production use, beyond trial or minimal use. So I wouldn't call it open source without a big asterisk.

In practice, its documentation says a self-hosted server runs on a free plan with 5 users, including all PDF tools, the API and single sign-on. Past that, the Team plan is $99 a month for 100 users. The website also describes the free tier as for individual use, and I couldn't find a clear statement on business use. If you're going to rely on it, ask Stirling in writing.

Which one?

My pick is BentoPDF. It does nearly everything an office uses Acrobat for, it's properly open source and your files stay on your own computer. The main drawback is that it won't feel as polished as Acrobat on a tricky document.

• Acrobat-style tools for the whole office: BentoPDF.
• Just merging and splitting: PDFsam Basic.
• Automating PDFs through an API, and happy with the licence: Stirling PDF.

The UK angle

• Mind what you upload. Contracts, payslips and HR letters are full of personal data, and under UK GDPR you need to know who is handling it. Free PDF websites are the real risk here, far more than Adobe.
• Adobe is fine for most firms. It's a big, established vendor, and US-based tools suit most small businesses. Don't switch for that reason alone.
• Local processing is a simple answer. With BentoPDF and PDFsam, the file doesn't go anywhere, so there's nothing to explain.
• Redact properly. Black boxes drawn over text can sometimes be lifted off. Use a real redaction tool, and check the result.

Honest drawbacks

• Fidelity. Adobe created the PDF format. Editing complex documents with embedded fonts or odd layouts is where free tools are most likely to let you down.
• No Adobe ecosystem. There are no Adobe e-signature workflows or Creative Cloud links. For sending contracts round for signature, see my DocuSign alternatives page.
• BentoPDF does its work on your computer, so large files lean on that machine's memory rather than a server.
• Licences need reading. Both BentoPDF's dual licensing and Stirling's split are less simple than "free".
• Support is limited. With the open versions, help comes from community forums and GitHub.

If you need PDFs generated, filled or stamped automatically inside your own software, the team at Dev Partners can build it.

Sources

• BentoPDF on GitHub
• BentoPDF licensing
• PDFsam Basic
• Stirling PDF on GitHub
• Stirling PDF licence file
• Stirling PDF engine licence
• Stirling PDF plans and licences
• Stirling pricing
• Adobe Acrobat UK business pricing