Stirling PDF Privacy Guide: Local-Only Mode, Self-Hosting and Secure PDF Redaction

The privacy problem Stirling is aimed at​

XDA's author lays out an awkward choice. Acrobat Reader is free for reading and signing. Redaction is reserved for Pro, which the author prices at about $20 a month. Adobe's free online tools process files by uploading them to Adobe first. So you either pay to work locally or upload the very document you wanted to protect.

Adobe's plans page backs up the feature split. Adobe lists redaction, comparing PDFs and turning scans into searchable PDFs among the extras in Acrobat Pro, not Standard. The "$20" figure is a rounded price. It matches the annual-billed-monthly Pro rate and is not a universal price. Standard costs less, and month-to-month pricing is higher.

What Stirling PDF 3.0 added​

Stirling PDF 3.0.0 shipped on September 24, 2026. The release introduced the "PDF Processor", which runs existing tools across large numbers of files from sources such as folders, FTP and S3, and keeps listening for new files. Heise also reported a revised text editor and OAuth SSO. Heise noted the processor is reached in the browser and is not directly available in the desktop app. That fits XDA's account of a browser dashboard and a simpler folder button on desktop.

3.0 is no longer current. The release list now runs through 3.0.1 (a Windows desktop hotfix), 3.0.2, 3.1.0, 3.2.0 and 3.2.1. Stirling-PDF 3.0.1 fixed a Windows desktop double title bar and temporary log files that kept growing. Windows users should install the latest build, not 3.0.0.

Local does not automatically mean private​

Stirling's own documentation separates three setups:

• Desktop, Local Only mode: Per the project FAQ, nothing leaves your computer, and a tool that can't run locally is blocked rather than uploaded.
• Stirling Cloud: Tools such as compress, OCR and convert send the file to Stirling's servers and return the result.
• Self-hosted server: Tools run on your organisation's server.

XDA's author says there is no dedicated switch for local mode. You simply don't sign in at first launch. Tools that need a server carry a cloud icon. If you sign in, those tools send files to Stirling's servers. In Local Only mode they are blocked, which rules out OCR and Office conversion. I could not confirm in the project docs that "don't sign in" is the only route into Local Only mode. Check which mode your app is in before you open anything sensitive.

Self-hosting with Docker​

The official guide calls Docker the recommended way to run a server. Its example maps port 8080 and mounts folders for configs, logs, custom files, the pipeline, storage and OCR language data. The standard image includes LibreOffice, Tesseract, OCRmyPDF and Ghostscript, among other tools, and the guide suggests 4 GB of memory. A "fat" image adds a bundled AI engine that stays off until you enable it, with 6 GB suggested. The guide also offers an ultra-lite image with core tools only and no OCR.

The caveats matter for security-minded readers:

1. Pin a version. The latest tag moves with every release. Use a version tag if you want to control upgrades.
2. Change the default login. The quick start signs you in with default admin credentials. Replace the password straight away.
3. Keep login enabled. The docs show how to turn it off, but doing so on a reachable machine exposes your documents.
4. Use HTTPS if the service is reachable from anywhere beyond localhost.

Self-hosting tells you where the service runs. It says nothing about whether it is configured safely.

Redaction: a black box is not enough​

Redaction is the headline feature for sensitive documents. XDA says Stirling's Redact can find every instance of a word and black it out, or let you draw boxes by hand. The project documentation says redaction permanently deletes the selected content and recommends keeping the original. It supports regular expressions and whole-word matching. It can also convert redacted pages to images so the text can't be selected or searched.

A practical routine:

1. Keep an untouched copy of the original.
2. Apply the redactions, and use the image-conversion option if the document is going outside your organisation.
3. Open the output and try searching for and copying the redacted text.
4. Only then share the file.

Release 3.2.0 also added a "Match Case" option to auto-redact, off by default, and made a redaction fail if the engine could not verify it. That is worth knowing if you redact in bulk.

Where the "does everything" claim falls short​

• Editing fidelity. XDA notes that if the embedded font lacks a character you type, the editor falls back to Helvetica. Stirling's docs likewise warn that fonts and layout can shift.
• OCR. The docs say desktop OCR usually needs Stirling Cloud or a server. Fully local OCR means self-hosting, and that is a trade-off for anyone who wants a purely offline desktop.
• Automation limits. The Processor's folder triggers have rules. Hidden files, symlinked folders and files still being written are skipped. Administrators must also allow the folder path.
• Usage allowances. The 3.0 release notes say automation includes 1,000 PDFs per month free, applying to Processor, API and AI use. AI is optional, off by default, and can use self-hosted models. XDA's separate claim of 1,000 monthly credits on Stirling's hosted AI is the author's own. The release notes describe the allowance differently, so treat the exact numbers carefully.
• Author's experience. The XDA author's observation that files started getting tagged "HR" automatically is a single user's report. I could not verify it. It suggests checking what runs in the background after onboarding.

Acrobat also still has things Stirling doesn't claim to match. The author concedes that people whose whole job lives in PDFs may still want it. Adobe's page lists the Action Wizard and Microsoft 365 integrations among its automation features.

Bottom line​

Stirling PDF is a credible free, open-source way to redact, merge, compare and sanitize PDFs without handing files to a cloud service. The privacy benefit comes from choosing the right mode, not from the brand. For sensitive work on Windows:

• Use Local Only desktop mode, or a properly secured Docker deployment.
• Avoid signing in if you want zero uploads.
• Update beyond 3.0.0.
• Verify every redaction before the file leaves your machine.

Whether it "replaces Acrobat" depends on how heavily you rely on Acrobat's workflows. For occasional private redactions, it does the job without a monthly fee.