This group gathers reading and writing utilities outside the main categories, with a strong lean toward PDF tools: viewers, editors, annotators and converters. It also includes reference managers, a tabular data viewer and readers for older formats like CHM.
Preview covers basic PDF work, but editing text, annotating heavily or exporting notes often needs more. PDF Expert is a popular paid editor, and Highlights is a PDF reader built for research that exports annotations. Zotero is a free, open source reference manager for collecting and citing sources, and Tad views CSV and other tabular data. Check whether editing features require a subscription.