--- title: "< font name > refers to non-standard font type \"application/x-font-ttf\"" description: This validation error occurs in EPUB 3 files. The .tff extension indicates that the font is a TrueType font. These types of fonts are no longer supported in EPUB3 files. In the IDPF guidelines, the fo --- [Skip to content](https://help.publishdrive.com/font-name-refers-to-non-standard-font-type-application/x-font-ttf#main-content) English Show submenu for translations [More support](https://help.publishdrive.com/kb-tickets/new?hsLang=en) ![pd-white.png\]](https://help.publishdrive.com/hs-fs/hubfs/pd-white.png?height=38&name=pd-white.png) Open main navigation Close main navigation - English Show submenu for translations - [More support](https://help.publishdrive.com/kb-tickets/new) - Go to publishdrive.com Go to publishdrive.com Hello. How can we help you? - There are no suggestions because the search field is empty. 1. 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