Absolutely yes! Reading Pdfs on smartphones is a kind of self-torture : if you zoom in  you get horizontal scroll. This little thing delivers the cure: it makes with few clicks 100% responsive epub. Usually one doesnt need such tool - books are managed on desktop with calibre or the like. But if en route  just now downloaded something and dont want to break eyes - this app is the tool to help out. Disclaimer: dont tested it with image based pdfs.