Adobe Acrobat and Smallpdf, answered by a self-hosted Java web application: Stirling PDF processes every file with its 60+ tools on your own server and deletes it after the task completes. Nothing is uploaded to a third party, which is the whole point for contracts, invoices, and medical records. The toolbox covers page operations (merge, split at page numbers or scanned dividers, rotate, reorder, crop, extract), conversion in both directions between PDF and Word, Excel, PowerPoint, images, HTML, and Markdown, OCR that turns scans into searchable PDFs via Tesseract/OCRmyPDF (including PDF/A archival conversion), and security tools for passwords, permissions, watermarks, signatures, and true UI-driven text redaction. A built-in viewer handles annotation, drawing, and text or image insertion, and V2 added stateful processing - upload once, chain multiple tools - plus undo/redo history. For automation, nearly every tool has a REST API endpoint, no-code pipelines combine operations into custom logic chains, and watched folders process files automatically. Enterprise deployments get SSO, user management, and audit logging; the interface ships in 40+ languages. With 84K+ GitHub stars it is the most popular PDF tool in self-hosting, replacing $20/month Acrobat subscriptions with flat infrastructure cost.

The ad-riddled "free online tools" sites people paste sensitive text into and upload confidential PDFs to - OmniTools replaces that whole ecosystem with one self-hosted app. It bundles 50+ utilities behind one clean React/TypeScript interface: image tools (resize, convert, crop, edit), video and audio tools (trim, reverse, convert), PDF tools (split, merge, edit), text and list utilities (case converters, formatters, shufflers), plus date/time, math, and data-format helpers for JSON, CSV, and XML. The architectural decision that makes it trustworthy is that all file processing happens entirely client-side in the browser - the server only serves static assets, and nothing you process ever leaves your device. That design has a pleasant side effect: the host needs almost no resources (people run it on a Raspberry Pi Zero), because your browser does the work while the server just delivers files. The Docker image is a remarkable 28 MB, making it one of the fastest apps to deploy and cheapest to keep running. There are no ads, no tracking, no accounts, and no upload limits. With multi-language support and an MIT license, it works equally well as a personal toolbox or a team-wide internal utility portal - one URL that replaces a bookmark folder full of questionable converters. Actively developed with 50 contributors and 9,500+ GitHub stars.

Serious readers organize, convert, edit, and serve their e-book libraries with Calibre - the definitive open-source e-book manager. This deployment runs the full Calibre desktop application on your server, accessible from any browser, so your library lives in one authoritative place instead of scattered across devices. Its conversion engine is the best in the business, translating between every major format - EPUB, MOBI, AZW3, PDF, DOCX, and dozens more - with fine control over fonts, margins, metadata, and structure detection. Metadata management downloads covers, descriptions, series info, and identifiers from online sources, and every field is editable in bulk. Beyond cataloging, Calibre includes a full e-book editor for EPUB and AZW3 internals, a news engine that fetches newspapers and magazines from the web on schedule and converts them into e-books, book comparison tools, and device syncing that sends the right format to each connected reader. The built-in content server exposes your library over HTTP so phones, tablets, and e-readers can browse and download remotely. A deep plugin ecosystem extends everything - metadata sources, format support, store integrations. For power users, the complete CLI (calibredb, ebook-convert) enables scripted library automation. Your books, your metadata, your server - permanent and DRM-free storage under your control.