Which is the most appropriate tool for my usage ?

I get annotated notes before the lectures. I want to import them as images into markdown so I can write between the images as bullet points or add new images.

I am confused between Typora, Obsidian and Zettlr

It would be nice if notes are stored in file system directory and can be easily exported to PDF.

I’m not familiar with the other two apps you list, but Obsidian can do what you’re asking for for sure