3 ms·

Which reasons?

• egypturnash 8y ago
  PDFs don't reflow, for starters - have you ever tried reading a PDF of a book on your phone? It's a miserable experience.
• gnicholas 8y ago
  In addition to reflow, described elsewhere, imagine having to design PDfs in a zillion sizes so it looks good on everything from an iPhone SE up to an iPad Pro (or iMac, for that matter).