What Is Stirling PDF?

Updated

Stirling PDF is a free, private PDF editor that you can run on your own infrastructure. According to the project's site, it has passed 31 million downloads and is used by 75% of the Fortune 500. The core distinction from most PDF tools is where the work happens: Stirling runs on your machine or your servers, and its source code is public, so files don't have to be uploaded to a third-party website to be edited.

That makes it most relevant if you handle sensitive documents, need to process PDFs in bulk, or want PDF operations callable from your own systems. If you only occasionally edit a PDF and don't care where it's processed, a browser-based tool may be simpler.

What Stirling PDF does

The site groups its capabilities into three levels:

Tier What it covers
PDF Reader Fast reading and simple tools for casual use
PDF Editor 60+ tools for editing PDFs on any computer or server
PDF Processor Classify, standardize, and route thousands of PDFs at once, fully automated

So the same product spans a single person annotating one file and a pipeline that ingests hundreds of documents unattended.

Why "private" and "open-source" matter here

The site's argument is direct: protect sensitive files from landing on websites you can't trust. Because Stirling's editor runs on your machine and the source is public, you can verify what the software does rather than taking a vendor's word for it. The page describes it as "private, open-source, and audit-ready," and notes it is validated by security experts.

If your constraint is a policy that documents cannot leave your network, self-hosting is the feature that decides the choice — not the tool count.

Automation and scale

For batch work, Stirling offers:

  • Pipelines — chain operations into a single run, and process file batches programmatically.
  • APIs & MCP — every PDF operation callable from your own systems; one request in, processed files out, with webhooks when it's done.
  • Policies — your rules applied the moment a file arrives.
  • Connectors — integration with tools your team already uses.

The example on the site shows a POST to /api/v1/pipelines/intake processing a zip of 412 PDFs. Typical pipeline steps listed include OCR on scanned pages, classification by type and sensitivity, signature validation, redaction, compression, and routing to a destination like SharePoint.

Two governance details are worth noting for regulated work: rule changes need approval, and every action is logged. The processor also reads scans, not just digital files.

The built-in assistant

For an open file, you can ask the assistant to make an edit in place — redact, translate, summarize, convert — while you watch. The site's example: a request to redact all account numbers returns "I made 14 redactions across 9 pages. Please review them in the canvas." The review step matters; the assistant proposes, you confirm.

Deployment and getting started

Stirling can run on any infrastructure, which is the point of the self-hosted model. The site offers a free trial and documentation, with pricing listed separately. Whether a paid tier is required for your use case depends on the plan details on the pricing page — the free editor and the scale-out processing features are presented as part of the same product, so check the pricing page before assuming a specific feature is included at no cost.

Choose Stirling PDF if you need PDF editing that stays on your own infrastructure, want to audit the code, or need to process PDFs in bulk through APIs and pipelines. Look elsewhere if you want a zero-setup web tool and have no requirements about where files are processed.