I failed to find how to create notes (it should be able to create and interlink all kinds of them if it's meant to be a knowledge repository: notes attached do

I failed to find how to create notes (it should be able to create and interlink all kinds of them if it's meant to be a knowledge repository: notes attached do a particular document, attached to a particular place in a document and not attached to anything, all notes should be taggable). Lack of support for any formats other than PDF (it should at least support EPUB, all other formats if possible: AZW, DJVU, FB2, Markdown, single-file HTML) limits its usage for studying e-books. And it's annoyingly slow (but I'd consider this tolerable if it was really helpful). I just hope this is just the beginning and Polar is actually going to improve.