Formatter can reference fonts from external sources. Externally referenced fonts are always embedded.
The text in the following block will be in the font EXTERNAL-LOBSTER which is referenced from a public dropbox link
This text is in the EXTERNAL-LOBSTER font
Code to include external font:
<@font-face font-family="EXTERNAL-LOBSTER" src="url(https://raw.githubusercontent.com/google/fonts/main/ofl/lobster/Lobster-Regular.ttf)" />