PDF Tools

Stirling-PDF94.8k★

Stirling-PDF is a self-hosted PDF toolbox: merge, split, edit, sign, redact, OCR, convert and compress, from a web UI, desktop app or REST API, without uploading files to someone else's server. It's the go-to self-hosted answer to Adobe Acrobat, Smallpdf and iLovePDF, and free for small offices. One docker run gets you going. Login, user management, the AI engine and the desktop frontend are proprietary; the rest is MIT. Security fixes ship often (a critical admin-only RCE plus file-read and SSRF bugs this year), so keep it updated and off the open internet. The free plan caps at 5 users, enforced in code. API-key calls, automation pipelines and AI draw on 1,000 processing units a month; clicking around the UI never counts. Team is $99 a month for 100 users and makes API calls free. Solo and small offices: free. Bigger teams or bulk scripting: budget for Team. The catch: the license went from Apache to GPL to MIT to MIT plus proprietary directories in under three years, and the proprietary license says production use needs a paid license while the pricing page sells a $0 Free plan. If that gap matters to your legal team, ask before you deploy.

KillerPDF4.2k★

KillerPDF is a free Windows PDF editor that covers what most people open Acrobat for: annotate, fill and sign forms, merge, split, reorder pages, OCR scans into searchable PDFs, compare two versions, print and flatten. GPLv3, no account, no telemetry, and processing stays on your PC. Install it with winget install killerpdf, Chocolatey or the Microsoft Store, or grab the portable build that carries its own .NET runtime. OCR runs on bundled Tesseract, signatures work with a Windows certificate or .pfx file, and there's even a command line for batch jobs. No paid tier exists. Solo users and small offices on Windows: free. Larger orgs can push the installer machine-wide, but there's no vendor support contract; that's what Acrobat and Foxit still sell. The catch: editing existing text is a cover-up, literally. It drops an opaque box over the old words and a new text box on top, and the help page says the original text stays in the file. Don't use it to hide anything: Save Flattened (pages become images) or use a real redaction tool like Stirling-PDF. It's Windows 10/11 x64 only, a young project with one main developer, and it checks GitHub for updates by default.

pdfx1.1k★

pdfx solves a small, annoying problem: bundling several PDFs into one file that still opens normally everywhere. It defines an open format that stores multiple PDFs inside a single, backwards-compatible PDF using an embedded manifest, and ships desktop viewers for Windows, Mac, and Linux to read and build them. Open any pdfx file in a regular PDF reader and it still works; open it in the pdfx viewer and you get the separate documents back. It is MIT-licensed and free. It is an Electron desktop app, so installing it is a download, not a project. The format itself is documented in a spec, which matters more than it sounds: a bundle-multiple-files feature is only useful if the format outlives the app, and a written spec means someone else could implement a reader if this project stalls. There is no server, no account, nothing phones home. If you regularly hand off sets of related PDFs (a contract plus its exhibits, a report plus appendices) and want one file instead of a zip, this is a clean, free way to do it. It is not trying to be Acrobat. For merging PDFs into one flat document you already have a dozen free options; pdfx is specifically for keeping them separate-but-together inside one file. The catch is adoption. The format only round-trips for people who also have a pdfx viewer; everyone else sees a normal single PDF and never knows the extras are there. As a personal organizing tool, fine. As a way to send structured bundles to clients, they need the viewer too, and most will not install it.

make-look-scanned841★

make-look-scanned takes a clean digital PDF and degrades it on purpose, so it looks like it came off an office scanner. Skew, grayscale, paper tone, scanner grain, soft focus, edge shadows, JPEG artifacts. The kind of imperfections that say a human ran this through a machine instead of exporting it from a template. Free and open source under AGPL-3.0. It runs three ways. There is a Go CLI for batch work, a browser version that does everything client-side via WebAssembly, and a single self-contained HTML file you can save and run offline. Nothing gets uploaded; the whole pipeline rasterizes each page to an image and reassembles it locally. Output is deterministic by default, so the same file produces the same result every time. This is a single-purpose utility, and it does its one job cleanly. If you need to submit a signed document that is supposed to look physically handled, or you are testing how a system copes with scanned input, this beats fiddling with image filters by hand. Free for anyone, no account, no limits. The catch is in the output. Because it rasterizes every page to an image, the result has no selectable text, exactly like a real scan. That is the point, but it means you cannot search or copy from the file afterward. And AGPL-3.0 is worth a look if you plan to fold it into a commercial service.