how do I add additional fonts
How is this question associated to LibreOffice?
Read this
- https://www.wikihow.com/Install-Custom-Fonts-in-Ubuntu
- How to add new fonts in Linux Mint (Ubuntu) – Linuxforever
- How do I install fonts? - Ask Ubuntu
- 3 Ways to Install TrueType Fonts on Ubuntu - wikiHow
- https://www.linux.com/tutorials/how-manage-fonts-linux/
or any other of the plenty links resulting from a web search.
Fonts are managed by the operating system - so turn to your operating systems documentation on how to install new fonts. Just be aware that PS Type 1 fonts are not supported with LibreOffice (starting with version 5.3)
Hint: For me on Ubuntu 19.10 double click on the .otf or .ttf file is sufficient to start application font-viewer and clicking Install button to install the font(s)