最近在用一个 PDF reader for macOS：Skim
https://skim-app.sourceforge.io/index.html

> It is designed to help you read and annotate scientific papers in PDF, but is also great for viewing any PDF file.

Features:
- 开源
- 还算合格的标注功能
- 记忆上次关闭文件时的位置
- 打开几百页以上的 PDF，加载页面比 Preview 快很多
- 查看所有的笔记和高亮