@CandyLords Thanks for your suggestion, I can see this feature being useful. However it is unlikely to be implemented any time soon for technical reasons. At the moment the selection of fonts is included with the applications. Opening this up for user upload would mean somehow storing font files with the user account, which in our end-to-end encrypted setup would mean re-downloading the fonts each time the document is opened. This alone could be overcome but real problems would arise when other users would open the document as they would not be able to download and decrypt the fonts uploaded by another user.
Long story short this feature is not present in OnlyOffice as far as I'm aware, but it's even less likely to be added to the CryptPad integration because of our privacy focus.