PDF format is not necessarily available on all mobiles. PDF readers tend to use themselves too much space and requires frequent updates, or frequently contain too many ads (some of them even require to have an Internet connection before using them, as they want to share what you download and extensive profiling data for who is reading documents that these apps actually did not create, and then insert targetted ads related to the PDF contents.
If one wants really mobility (i.e. offline reading) there are better formats that are less intrusive, and whose readers are both safer, with much less unnecessariy plugins such as online form editors or cloud printing or reshares on social networks.
"ebooks" formats (or core HTML, not requiring active scripts and online APIs, or even TXT) are usually better suited for mobility: they have the advantage of being suitable for all screen sizes (not the case of PDFs whose page layout is static, and that requires constant zooming, and horizontal panning to read them on most smartphones: a PDF is only suitable on smartphones for a single page (letter or A4 max). Even MS Office .doc[x] are easier to use on smartphones (there's a free viewer for it, and it's really small, faster and much more secure than most PDF readers, including the Reader made by Adobe, and which is still not workiong correctly on many smartphones as they require excessive privileges or frequently depend on tricky/unsupported/unstable APIs of the mobile OS, or are supproted only on the most recent versions of these OSes; Adobe Reader for smartphones is also too frequently targetted by third party apps that want to modify its behavior by adding their own hooks that Adobe Reader uses without any question)!
I don't have any PDF reader on my smartphone. I have only the old one that was preinstalled but that I have blocked completely (againsst all updates and all its autostarted services). If I need a PDF, I'll download and read it on my PC, or I'll save it to Google Drive and Google will render it and allow me to view it without activating many services and third-party plugins. This is rare: I do that only to view some billing or purchase order, but I won't store any PDF on my smartphone.
MediaWiki should better support the exports as eBooks formats, but the PDF format is the worst one for mobiles, including in terms of accessibility.