Oh, I love this! 一見鍾情

1. Select some text in the PDF.
2. Click on a color on the toolbar. This creates a link.
3. Paste into any note. Remember to press RETURN. Voila! See the pasted result become a nice color box.
4. Hover over a link to get a popup preview of the context.

Quick verdict: 4/5

Cons

Does not work with:

OCRed PDF book with vertical text e.g. Chinese

The performance there is much worse than Obsidian plugin - Annotator｜PDF註記插件. It's practically unusable.

Issues

Mouse selection sticky

On one occasion, my mouse selection goes berserk: it slips and ends up selecting more text than intended as I navigate the context menu.

Solution

Restarting the computer worked. Glad it's only a one-off anomaly.

Auto-paste needs extra new line at the end to avoid gluing together successive quotes

Discovering the problem

Solution

Guided by forum, made my YT self-guide

More ...

Combining PDF reading, annotating, backlinking for context, and flashcarding 一邊閱讀筆記一遍建立閃卡