You can add and use custom Fonts in a CustomShow. 

From the Admin Settings you can choose to show Default Fonts and Custom Fonts or you only wants to show Custom Fonts in your CustomShow Editor which should be used through out as per your brand guidelines. 

This is the best way to stick to your branding. 

While uploading Font you need to make sure that Font is not available in your Font list already. 

You cannot add an existing font again. 

You can add complete Family of Fonts under one title. Whenever you upload a CustomShow for the first time, you have to upload all the Fonts used in that CustomShow. 

Make sure to add Regular, Bold and Italics Font separately. 

Please check the steps below to add Custom Fonts.