Okular is an open source software application for reading, viewing, and annotating PDFs, eBooks, and other documents. It is available for Linux, Windows, macOS, iOS, and Android. It is a versatile tool for reading, annotating, and sharing documents. Its user interface is highly customizable, allowing users to customize the look and feel of the software to suit their needs. The app also includes a variety of features, such as support for text search, highlighting, and annotations. Okular also supports the integration of digital rights management (DRM) so that documents can be securely shared with others. In addition, Okular is designed to work with a variety of file formats, including PDF, OpenDocument, ePub, XPS, DjVu, CBR/CBZ, and many more.
Sumatra has no comments and fill in the form functionality as Okular has.