[opensourcedex]

KillerPDF is a free, open source office suites project written in C# and released under GPL-3.0. It has 3,879 GitHub stars, 307 forks and 38 open issues, and was last pushed 4 days ago. On this registry it ranks #7 of 11 tracked projects in Office Suites, with 5 head-to-head comparisons available.

What is KillerPDF?

KillerPDF is a free, open-source PDF editor for Windows, built in C# under the GPL-3.0 licence, that gives individuals and teams a complete view-annotate-OCR-edit-sign workflow without an Adobe subscription and without sending document processing off the machine.

What it is

KillerPDF is a native Windows desktop application for reading, editing, and producing PDF documents, released as open source under GPL-3.0 and developed as a C# / .NET monorepo. It ships its own PDF 2.0 processing engine, The KillerPDF.Engine, which is a reusable .NET library for PDF 2.0, PDF/A, and PDF/UA documents with a public API, tests, corpus tooling, and separately documented release history. Rendering is handled by PDFium, and the application covers the full document lifecycle: viewing, annotation, optical character recognition, page organisation, form filling, digital signing, printing, and flattening.

The concrete problem it solves is the recurring cost and the data-handling constraint of commercial PDF tooling. Editing, annotating, OCR, merging, splitting, signing, and opening password-protected files normally require a paid Adobe Acrobat subscription, and cloud-based alternatives require uploading confidential documents to a third party. KillerPDF replaces that subscription for Windows users while keeping document processing local, with no account and no telemetry. It also replaces ad-hoc scripting for repetitive document work by exposing every core operation as a headless command line, so the same engine that powers the GUI can run unattended in batch jobs.

Key capabilities

  • PDFium rendering with four view modes (Single, Continuous, Two-Page with a book layout option, and Grid), tabbed documents, and a split pane for viewing two documents side by side.
  • Built-in OCR via bundled Tesseract with no cloud dependency: produce searchable PDFs, OCR a page or region to the clipboard, extract all text, and download extra languages on demand.
  • Annotation with inline text editing and font matching, word-wrapping text boxes, drawing, lines, highlights using the Multiply blend so underlying text stays readable, images, and page-number or watermark stamps, with per-tab undo and redo history.
  • Page organisation covering merge, split, insert, rotate, crop, extract, delete, and drag-and-drop reordering, plus page or multi-page export to PNG or JPEG, and merging by dropping a folder or .zip onto the window.
  • Form filling for text, checkbox, radio, and comb fields as live controls saved back to the file, alongside digital signatures using a Certum SimplySign cloud certificate and drawn or imported signatures and initials.
  • Headless command line for every core operation, including KillerPDF.exe --merge, --extract-pages, --split, --decrypt, --to-image, --flatten, --print, --ocr, and --batch-resave, with meaningful exit codes that work even while the GUI is open.
  • Standards-safe saves validated against a 2,900-file veraPDF conformance corpus under a zero-regressions requirement, with results published in validation/RESULTS.md.

Who uses it and how

  • Windows users who need a full PDF editor without a recurring subscription, using the compact installer for per-user or machine-wide deployment.
  • Locked-down or offline environments where the self-contained portable edition, which bundles its own runtime, can run without a system-wide install.
  • Document-heavy teams processing scanned paperwork, using bundled Tesseract OCR to turn image-only scans into searchable, extractable text.
  • Automation and scripting workflows that call KillerPDF.exe from batch jobs for merges, splits, decryption, image export, and bulk resaves with a CSV log.
  • Multilingual offices, supported by a localised interface in 15 languages including Kazakh and Russian, with translations contributed through TRANSLATING.md.

Getting started

Download the compact Windows installer or the larger self-contained portable edition from KillerPDF.net. No package manager, Docker image, or hosted service is referenced; installation is the installer or the portable executable.

How it compares

Against Adobe Acrobat and similar subscription editors, KillerPDF is licensed under GPL-3.0 rather than sold per seat, so there is no recurring cost to remove. It processes documents entirely on the local machine with no account and no telemetry, instead of tying the workflow to a vendor account and cloud upload. Its command line and portable edition also suit unattended and restricted environments that subscription desktop tools do not target.

When to use it — and when not to

KillerPDF is Windows-only, so anyone working primarily on macOS or Linux should look elsewhere. It is a desktop application, so there is no database, object storage, or SMTP service to operate, but optional startup update checks contact GitHub and are enabled by default, and they can be turned off in About or the update dialog. GPL-3.0 means the licence is copyleft, which matters if the engine is to be embedded in proprietary software; prospective users should also weigh the 38 open issues and confirm the documented limits on the technical page before committing a large workflow to it.

project readme (upstream, from github) — read inline

KillerPDF is a free, open-source PDF editor for Windows. View, annotate, OCR, merge, split, edit text, draw, sign, fill forms, print, flatten, and open password-protected PDFs without an Adobe subscription. Choose the compact Windows installer or the self-contained portable edition. Document processing stays on your computer, with no telemetry.

Full how-tos live on the help page; internals, formats, and limits on the technical page.

The KillerPDF.Engine

KillerPDF 1.8 introduces The KillerPDF.Engine, an independent and reusable .NET library for PDF 2.0, PDF/A, and PDF/UA document processing. It is a first-class area of this monorepo with its own public API, tests, corpus tooling, architecture documentation, README, and release history.

Features

  • High-quality PDFium rendering with four view modes (Single, Continuous, Two-Page with a book layout option, Grid), tabbed documents, and a split pane for two documents side by side
  • Annotate with inline text editing and font matching, word-wrapping text boxes, drawing, lines, highlights, images, and page-number or watermark stamps. Highlights use the Multiply blend so the text underneath stays readable, and every tab has its own undo and redo history.
  • Built-in OCR (Tesseract bundled, no cloud): make searchable PDFs, OCR a page or region to the clipboard, extract all text; extra languages download on demand
  • Organize pages: merge, split, insert, rotate, crop, extract, delete, drag-and-drop reordering; drop a folder or .zip onto the window to merge its contents
  • Export one page or a multi-page selection as PNG or JPEG directly from the Pages panel
  • Transform: rotate, scale, flip, deskew by drawing a level line, perspective correction for photographed pages, and a LEVELS section (black point, white point, midtones) for pale scans
  • Forms: fill text, checkbox, radio, and comb fields as live controls and save back; digital signatures with a cloud certificate (Certum SimplySign), plus drawn or imported signatures and initials
  • Print with a real in-app preview, paper size and source selection, scale / position / margins / pages-per-sheet options at 300 DPI; Save Flattened rasterizes to a fully uneditable PDF
  • Full-text search with highlighting, and column-aware text selection that copies multi-column pages in reading order
  • Night-mode inversion works independently in each split pane. Thirteen themes, live accent colors, and toolbar styles provide 33 looks, while the resizable sidebar can dock on either side.
  • Localized UI in 15 languages, including Kazakh and Russian (contribute via TRANSLATING.md); full keyboard shortcut overlay on F1 with list and visual keyboard views, a shortcut toggle, and an always-available Ctrl+Shift+K recovery chord
  • Opens password-protected PDFs (prompts instead of erroring) and repairs damaged ones
  • Separate standard and portable downloads: the compact installer supports per-user or machine-wide deployment, while the larger portable edition includes its own runtime
  • Standards-safe saves: every release is tested against a 2,900-file veraPDF conformance corpus with a zero-regressions requirement. See validation/RESULTS.md.
  • No account or telemetry. Optional startup update checks contact GitHub and are enabled by default; downloading and installing an update requires confirmation. Turn checks off in About or the update dialog. Extra OCR languages download on demand.

Command line

Every core operation also runs headless from a terminal, with meaningful exit codes, even while the app is open:

KillerPDF.exe --merge out.pdf a.pdf b.pdf scan.jpg
KillerPDF.exe --extract-pages in.pdf 1-3,5 out.pdf
KillerPDF.exe --split in.pdf pages\
KillerPDF.exe --decrypt locked.pdf open.pdf [--password p]
KillerPDF.exe --to-image in.pdf imgs\ --dpi 300 --format jpg
KillerPDF.exe --flatten in.pdf flat.pdf
KillerPDF.exe --print in.pdf --printer "HP LaserJet" --pages 1-4 --copies 2
KillerPDF.exe --ocr scan.pdf searchable.pdf --lang eng
KillerPDF.exe --batch-resave inDir\ outDir\ --log report.csv
KillerPDF.exe --help

Full reference on the help page.

Screenshots
KillerPDF comparing two PDFs side by side, with highlighted changes and a page-difference summary open
PDF comparison. Review highlighted differences and a summary of changed and missing pages.		 KillerPDF Transform preview with levels, color mode, DPI, output pixel dimensions, and JPEG compression controls
Transform output. Adjust page quality and see the output pixel dimensions for your chosen DPI.
KillerPDF in Two-Page view with highlighted text and a fillable text field on the right page
Fillable fields and annotations. Add and move text fields alongside highlighted document text.		 KillerPDF in Grid view with four view-mode buttons and the zoom menu in the footer
View and zoom controls. Switch layouts and choose a zoom level directly from the footer.

Requirements

  • Windows 10 or 11 (x64)
  • The standard installer uses the .NET 10 Desktop Runtime and offers to install it when needed.
  • The portable package includes the runtime and works offline without installation.

Download

WinGet:

winget install killerpdf

Chocolatey:

choco install killerpdf
  • Standard installer:
  • Portable edition:
  • Source (GPL3 corresponding source for this release):

Build from source

git clone https://github.com/SteveTheKiller/KillerPDF.git
cd KillerPDF
dotnet publish -c Release

Output lands in bin/Release/net10.0-windows/publish/. Normal publishing produces the development build plus a versioned KillerPDF--src.zip. The release pipeline builds KillerPDF.exe, a compact framework-dependent installer, and KillerPDF-Portable.exe, a self-contained offline edition. Installed shortcuts launch the inner app directly for faster startup.

KillerPDF 1.8 requires the .NET 10 SDK. Both the reusable engine and the Windows application target .NET 10, with the application using net10.0-windows.

The desktop document pipeline now uses The KillerPDF.Engine for document parsing, writing, editing, repair, forms, annotations, signatures, and preservation-sensitive page operations. PDFium remains the rendering backend, while PdfPig handles text extraction.

Translations

UI strings live in Strings/ (one XAML ResourceDictionary per locale). To add or improve a language, see TRANSLATING.md. Missing keys fall back to English, so a partial translation is fine.

Changelog

See the KillerPDF application changelog and The KillerPDF.Engine changelog.

License

GPLv3. See LICENSE. If you fork, modify, or redistribute KillerPDF, your version must also be released under GPLv3 with source available. No exceptions for commercial rebrands.

Frequently asked questions

Is KillerPDF free to use?

KillerPDF is open source under the GPL-3.0 licence. There is no licence fee and no seat count — you can self-host it or, where the project offers one, pay a vendor for a managed version instead.

What does KillerPDF do?

Free and open-source PDF editor for Windows with a built-in PDF 2.0 engine. View, annotate, OCR, merge, split, crop, rotate, compare, edit text, draw, sign, fil

What is KillerPDF written in?

KillerPDF is primarily written in C#. Its source is publicly available at https://github.com/SteveTheKiller/KillerPDF, and it has 3,879 GitHub stars.