Thanks Bluefrog for pointing to the annotation feature. I missed that somehow. As I understand it, this is designed to keep pdf and annotation file side by side, copying and pasting linked quotes from one to the other. I will try this at home on the big monitor, on the road with the iPad I am loosing quite some reading space. I‘ll try that too but my eyes these days are not as sharp as they used to be.
Initially I had in mind pulling several annotation files out of one pdf, all linked to its source and possibly to own thoughts on the topic. Like Zettelkasten. But that might just be a matter of taste.
While trying out the annotation feature I noticed another thing: to highlight or underline text, I do not have to activate the edit mode! Selecting text offers some tools for that directly. I didn’t catch that one as well, but it makes life much easier.