The Obsidian PDF++ plugin enhances the native PDF viewer in Obsidian by adding highlighting capabilities. It offers two methods for highlighting text: one that doesn't modify the original PDF file and another that writes annotations directly into the file. The plugin also includes Vim-like keybindings and supports link mode. Additionally, it is compatible with other plugins like Hover Editor and Better Search Views, while avoiding conflicts with Close Similar Tabs. With PDF++, users can easily highlight text in their PDFs, making it a valuable tool for research, note-taking, and collaboration.