You can add fonts when editing text in the builder. At this time only Google fonts are able to be imported into Woobox.
To import a font, click any of your text to edit then click the + sign at the top of your page.
Next, start typing a google font name and select the font you want when it populates.
Now it’ll be in your list of fonts and can be used in your offer.
Here’s Google’s site with their font previews and names: https://fonts.google.com/