Custom fonts are not yet supported in the DPS Preflight app that appears in the store. They are supported in a custom preflight app that you build. It's one reason to build a custom preflight app, along with the ability to see the app icon and launch images and to test push notifications. See this article for details on the different preview methods: Digital Publishing Solution Help | Preview content for DPS 2015
Custom fonts are not yet supported in the DPS Preflight app that appears in the store. They are supported in a custom preflight app that you build. It's one reason to build a custom preflight app, along with the ability to see the app icon and launch images and to test push notifications. See this article for details on the different preview methods: Digital Publishing Solution Help | Preview content for DPS 2015
Please be a bit more specific, are you asking about a custom preflight app you've built or DPS Preflight? Bob's asking about details related to this.
If you built a custom preflight app and fonts aren't working, then it's time to troubleshoot your font zip file, the font-manifest, and possibly the fonts.