Okular

Okular is a universal, open-source document viewer developed by KDE, designed for multi-platform use. It supports a wide range of formats including PDF, EPub, DjVu, Markdown, CBR/CBZ for comics, and common image formats like JPEG, PNG, and WebP. With features like annotation, form filling, and digital signatures, Okular is a flexible alternative to proprietary viewers such as Adobe Acrobat Reader, Foxit Reader, and SumatraPDF.

Key features include:

• Annotation Tools: Add inline notes, popup notes, highlight text, and underline text in PDF documents.
• Selection Modes: Copy and paste text or tables from documents.
• Magnifier Mode: Zoom in on small text for better readability.
• Content and Thumbnail Panels: Easily navigate documents using auto-generated tables of contents and thumbnail previews.
• Digital Signature Support: Verify digital signatures embedded in PDFs and sign documents.

Okular is suitable for users who need a comprehensive tool for reading, annotating, and managing various document types. It is particularly useful for students, researchers, and professionals who work with PDFs and other document formats regularly.