What it is
Stirling PDF is a self-hosted web app for doing things to PDFs: merge, split, OCR, convert to/from other formats, watermark, redact, fill forms. Drag a PDF in, click a tool, get a result. No account, no upload to a third party, no "free version watermarks your output."
Why I run it
The PDF tools world is a parade of either limited free websites that upload your file to who-knows-where, or expensive desktop apps. For one-off office-paperwork tasks — combining a few scans, OCRing a receipt, redacting a number from a screenshot — Stirling does all of it locally and doesn't ask anything in return.
The privacy framing matters here. PDFs I run through it sometimes contain things I don't want online: passport pages, contracts, tax forms. The whole point of doing this self-hosted is that those files never leave my hardware.
How I use it
Open the page, drag the PDF in, pick the tool, download the result. The UI is a tile grid of every operation grouped by category. I use the merge-PDFs, the page-extract, and the OCR tools more or less weekly; the more exotic ones (signing, redacting, form-fill) once in a while.
For "advanced" operations — OCR, ebook conversion, HTML-to-PDF — Stirling has a tiered dependency model. The slim image doesn't ship LibreOffice and Calibre; you opt in via an env var that triggers their install on first start. Larger image, slower startup, but you only pay it if you use those features.