Purpose

Currently Confluence only supports .ttf and .ttc font files for PDF export. The official support for .otf is currently tracked at  CONF-25187 - Getting issue details... STATUS . Please note that even though this is mark as resolved, the official resolution is marked as WON'T FIX which means that this is not supported.

Solution

1. Convert the .otf font file to .ttf or .ttc. There are a bunch of free converters available. Some that are known to work is http://www.freefontconverter.com/ and http://onlinefontconverter.com/

2. Upload the converted font as per described at Create a PDF in Another Language