[Quoth]

Calibre conversion, but a better idea is to install an epub reader on iOS and Mac. I Use Lithium on Android and Calibre Viewer on Linux. The Wiki here has a list of ePub apps for iOs. Many are the same as on Android. I've discarded some because they ignore the CSS and others because they "import" the ebooks and don't use the locations used by Calibre on the SD card (or internal storage), so they can't be managed by Calibre.

The Kindle apps are meant for ebooks purchased from Amazon, even more so than the actual Kindle ereader. You'd be better viewing the AZW conversion from ePub2 on an eink Kindle such as PW3. That will match what Amazon will deliver. If the epub2 has embedded fonts, then the azw conversion will have the fonts (or indeed Amazon KDP upload as epub2 and then purchased as AZW or KFX). You need to have embedded all the fonts on the epub2 converted from docx (I use LO Writer) in Calibre. Then on a real kindle select "publisher" in the Aa font menu. Works even on Kindle Keyboard.

I uninstalled the Kindle Apps from everything as they were periodically contacting Amazon even when the App wasn't open. As well when actually in use. Possibly a consequence of how KU and KOL are implemented. The KU and KOL cheat authors/publishers and track every page you read and so are not consumer friendly.

The Fire isn't a real Kindle, it's a partially locked Android tablet with a version of the Kindle App.