Apps to PDF annotation

Polar is a powerful desktop application designed to serve as an integrated reading environment. It allows users to actively read, annotate PDFs and web pages, create flashcards for spaced repetition learning, organize their digital library, and track their reading and learning progress. It's built for focused and deep engagement with digital content.

Document Viewer is a highly customizable and lightweight document viewer designed for Android devices. It supports a wide range of formats including PDF, DjVu, XPS, CBZ, CBR, and ePub, offering features like highlighting, annotation, and optimal performance.

SCIENTILLA is a free, open-source scientific register designed for researchers and organizations to manage bibliographies, references, and knowledge efficiently. It facilitates collaboration and streamlines the research workflow.

PDFedit is a free, open-source PDF editor targeted primarily at Unix-like operating systems users, including those running Windows with Cygwin. It offers core PDF manipulation functionalities like editing, merging, splitting, and basic form creation, though it lacks support for encrypted files or advanced text editing.

qpdfview is a lightweight, tabbed document viewer based on Qt. It supports PDF, DjVu, PostScript, and other document formats, offering features like annotation, form filling, and a clean, customizable interface for efficient document management.

Xournal is a classic open-source application designed for digital note-taking, sketching, and PDF annotation, primarily using a stylus. It provides a simple yet effective environment for handwritten notes and document markup, offering support for various input methods including Wacom tablets.

Skim is a free and open-source PDF reader and note-taker for macOS. Tailored for scientific use, it offers advanced annotation tools, robust export options, and tight integration with LaTeX, making it an ideal companion for academic research and professional document management.

JabRef is a free and open-source reference management software, primarily designed for LaTeX users, utilizing BibTeX and BibLaTeX formats for efficient organization and citation of academic references and documents.

Okular is a versatile document viewer from the KDE community, supporting a wide array of file formats including PDF, EPUB, DjVu, and TIFF. It offers intuitive navigation, robust annotation tools, and features like text selection and saving, making it a powerful tool for handling diverse document types.

Zotero is a free and open-source reference management software that helps users collect, organize, cite, and share their research sources. It integrates seamlessly with web browsers and word processors to streamline the research and writing process.