Format of choice for immediate offline reading, easy sharing or simple portability
PDF stinks for that. The ONLY plus of PDF is maintaining appearance of paper printout. So it's useful to electronically proof books, manuals, magazines and papers as well as other documents intended to be printed.
If the goal is immediate reading and portability, then eBook formats win. Or a responsive HTML document (Save As Web Page Complete). Except you need two, Mobi and ePub. Because Amazon are nasty. Calibre is your friend to convert Doc, RTF, HTML, ODT and SOME PDFs to ePub/Mobi/azw. The AZW format, like ePub, supports publisher fonts (mobi doesn't), but the publisher fonts etc only work well on newest Kindles.
PDFs need a giant screen unless they are designed for smaller than Letter/A4 documents. Also really slow for larger documents.
Adobe version of ePub readers that are age of Kindles with only basic mobi support work very well with publisher fonts. Some very old eInk and LCD readers.
PDF is now only of use for people preparing & proofing documents for paper publishing, not ordinary users. It needs to DIE as a document distribution method to the public. HTML or ePub is better for that.
PDF is primarily for paper, hence fixed layout. Now with people primarily reading on screens, (over 50% of eBooks on phones) and no standard screen size or resolution, like Letter and A4 on paper, layout needs to be "Responsive" and work with user selected rescaling (sharp vs poor eyesight).