Loop-PDF

A desktop PDF toolkit for editing, inspecting, validating, and automating PDF workflows.

Download · Platform support · Project guide · Build from source

New install? Get Loop-PDF from the official GitHub releases. Windows and Linux are supported for V1; macOS source builds are best-effort only.

What it does

• Edit and inspect PDFs with annotations, forms, attachments, optional content, text layout analysis, and document-structure tools.
• Protect documents with encryption, certificate management, signature validation, and digital signing.
• Optimize and compare files with compression, rendering, page operations, document comparison, and image/text extraction.
• Automate PDF work with PdfTool for batch pipelines, reporting, preflight checks, rendering, redaction, and more.

Choose the right tool

Tool	Use it for
LoopEditor	The primary interactive workspace for editing, inspection, and editor plugins.
PdfTool	Scripted and batch workflows in CI or from the command line. Run PdfTool help for commands.
Pages / Production workspace	Batch page geometry, assembly, and export through Core and PdfTool.
Document workspace	Quick, interactive PDF viewing and inspection in LoopEditor.
Compare workspace	Reserved product workspace over the Core comparison contract.

Known limitations

• The interactive canvas approximates overprint by default. The standard page renderer does not composite overprint (OP/op/OPM in the graphics state). When the current page contains overprint-bearing content, the canvas shows a persistent fidelity indicator naming the reason; one click on it switches that page to an authoritative, overprint-accurate render, and one click returns to the fast approximation. Preflight only raises a finding for the unsafe white/near-white overprint case — a document using ordinary overprint (spot-over-process, rich black over an image) produces no finding at all. Use the canvas indicator to check any overprint-sensitive page before it ships to print.

Install

Use Loop’s own release artifacts, not upstream packages.

• Windows (x64): download the MSI or portable ZIP from GitHub releases. V1 installers are unsigned — Windows SmartScreen will show an “unrecognized app” warning on first install. Choose More info → Run anyway to proceed. Verify the download against SHA256SUMS.txt on the release page before installing.
• Linux (x64): download the AppImage from GitHub releases, chmod +x it, and run. Verify the download against SHA256SUMS.txt on the release page. Flatpak packaging exists (LinuxFlatpak.yml) but isn't yet attached to releases. ci.yml also builds a .deb on every push to master, but it does not work — verified by installing it on a clean Ubuntu 22.04 container: dpkg -i succeeds, but the binary fails to launch (libQt6Gui.so.6: cannot open shared object file) because, unlike the AppImage, it doesn't bundle the Qt runtime, and it also has a glibc version mismatch against 22.04. Do not install the .deb until it's fixed.
• macOS: not supported for V1. There is no official package, notarization, or macOS CI coverage.

See platform support for supported configurations, package layouts, and current validation notes.

Build from source

Loop-PDF requires a C++20 compiler, Qt 6.11.1 or newer, and vcpkg. Windows and Linux are the supported development targets.

git clone https://github.com/mberrys/Loop-pdf.git
cd Loop-pdf

git clone https://github.com/Microsoft/vcpkg.git
./vcpkg/bootstrap-vcpkg.sh -disableMetrics
export VCPKG_ROOT="$PWD/vcpkg"

cmake -B build -S . \
  -DLOOP_INSTALL_QT_DEPENDENCIES=0 \
  -DCMAKE_TOOLCHAIN_FILE="$VCPKG_ROOT/scripts/buildsystems/vcpkg.cmake" \
  -DCMAKE_BUILD_TYPE=Release
cmake --build build

On Windows, use Visual Studio 2022 or MinGW. For the full set of build options and packaging requirements, consult CMakeLists.txt and the platform guide.

Documentation

• Platform support and packaging
• Repository map and upstream policy
• Preflight tool documentation
• Packaging and licensing guide
• Contributor and architecture guidance

Contributing

Contributions, testing, feedback, and bug reports are welcome. Please read AGENTS.md and the repository map before starting work, especially when changing the forked upstream codebase or syncing upstream.

License and acknowledgements

Loop-PDF is based on PDF4QT and is currently distributed under the MIT License. The license is subject to change at any time. It includes third-party components with their own license obligations, including Qt, FreeType, OpenJPEG, OpenSSL, Little CMS, zlib, libjpeg, and Blend2D. Review the packaging and licensing guide before distributing a build.

Copyright © 2026 Michael Berry. Portions are copyright © 2019 The FreeType Project.