Interesting, thanks for sharing.
I may have misunderstood, but it looks to me that it’s adding Obsidian-flavour highlights to PDFs, not standard annotations? (E.g. the highlights are only visible in the Obsidian viewer?) Which would make it an automatic no for me (I have a rule that I only undertake PDF annotations in the standard format so that it’s cross-compatible and not locked into the PDF or a specific app).
Otherwise it looks quite good, though DT does most this stuff natively (as does PDFExpert, which uses standard annotations and is cross-compatible).
That block highlighting function is useful in principle - a couple of apps offer it. I’ve yet to find a use case myself, but I understand why our mathematician friends and others might need it. (I’m either highlighting words, or I end up screengrabbing an entire diagram, so I’ve not made much use of the block highlight function.)