sioyek

Sioyek is a PDF viewer designed for reading textbooks and academic research papers, with navigation features that address the specific frustrations of that kind of reading. It runs on Windows, macOS, and Linux.

The features that set it apart from a general PDF reader are mostly about jumping around documents efficiently. Smart Jump lets you click on a citation or figure reference in the text and jump directly to that figure or bibliography entry, even if the PDF file itself does not contain embedded links. You can also send a bibliography item to Google Scholar or Libgen from within the viewer by middle-clicking on it. The Overview feature gives you a small pop-up window showing the referenced content without leaving your current position. Portals let you link two separate positions in a document together, so if a paragraph keeps referring to a figure many pages away, you can set up a portal and have the figure show in a second window that updates automatically as you read, which is most useful with a second monitor.

For tracking your place, there are two systems. Marks work like bookmarks keyed to a single letter, where lowercase marks are local to the current document and uppercase marks are global across all documents, following the same convention as the Vim text editor. Bookmarks are similar but named with text strings instead of single letters, and are always global. Highlights let you mark text in several colors and search across all your highlights later.

All key bindings and display preferences can be changed by editing plain text config files. The app can quickly search and re-open any file you have previously viewed.

Installation is available through official installers on the releases page, a Homebrew cask on macOS, and packages in the repositories for many Linux distributions including Debian, Ubuntu, Arch, NixOS, Fedora, and openSUSE. The README also includes build instructions for all three platforms if you prefer to compile from source.