For pdf files (even larger one) i would always choose a PocketBookdevice. It has a nice PDF-Reflow function, which works, depending on the formattin of the pdf-file, pretty well.
You have subfolderstructure on it, like any filesystem, because there is a linux system running on it.
You have search funtion in pdf-files and all other ebooks.
Its pretty fast in booting and switching pages.
If you need a screenshot of an pdf file of your choise, pn me that file
