Quote from the book "Как достичь цели. Четыре дисциплины исполнения"

Suitable for smartphones, Android tablets, e-readers (except Kindle) and many programs

Can be opened on almost any device

Opens in Adobe Reader

Optimized and suitable for smartphones

Suitable for Kindle e-readers and Android apps

Suitable for iOS devices (iPhone, iPad, iMac) and most reading apps

Development of FB2 format