They are, which is why the document reader costs $5 on Android and $15 on iOS
EPUB and web page reading we're planning to support once we drop support for everything before Android 4.4 - 4.4 replaced Android's old app-embedded web browser with Chromium, so it's a much better system to build around when working with HTML files (which technically is what EPUBs are too).
PDF we're waiting for a better PDF decoder library to appear - only one we've found so far that does Chinese well has punishingly high royalties, but Android L added native PDF decoding so we're hoping that may facilitate our adding PDF support.
DOC/DOCX/RTF support take advantage of iOS' built-in system for decoding those, so unless / until Google adds an equivalent (which doesn't appear to be coming in Android L anyway) it's unlikely we'll be able to do much for them.
Pagination we could theoretically add now but we've had relatively few requests for it so we feel like it can probably wait until we're ready to do some of those other updates.