Make sure you have the permission to embed the fonts into documents. To check this, right click on the font and select Properties; then click on the Details tab and verifiy the Font Embeddability permission is set to “Installable”.
Alternatively copy the font to the Fonts folder located in the Resources panel. This way the font is used from within the template and will travel to Workflow (make sure you own the font and adhere to the license of the font!). Underwater this generates the @font-face definition, this definition can be modified from within the user interface of the Designer. Choose: Edit > Fonts to invoke the Font Manager…
The font automatically becomes available in the various Fonts dropdowns (e.g. toolbar, Format menu, Text Formatting dialog). In CSS they can be referenced by the name specified in the Font Manager. For example: