There are 2 repositories under pdf-annotator topic.
A plugin for reading and annotating PDFs and EPUBs in obsidian.
A mind map, outline for obsidian,It support mobile and desktop
THE reference manager with features including PDF reading/annotating, Markdown/Excalidraw note-taking, project/note linking, and more...
Annotation layer for pdf.js (forked from instructure's pdf-annotate.js)
PDF format annotation and labeling support for Label Studio
Small Project of a PDF annotation tool written in C++