That’s not a font conversion, that’s an encoding/charset conversion, which is also a terrible (and subtle) bug.
I don’t know what “raw file” means in this context. Every file has an encoding.
Can you provide us with the file where this happened? (Or an example file that just exhibits the problem if this specific file is sensitive.)
If you’re uploading from a system that has the file command, can you show us the following (on the originating system):
file -bi name-of-file.txt
And, I guess we also want to see what it’s being converted to, so run that on the Virtualmin system, as well.
If you’re uploading from Windows, I would guess that’s where the problem is coming from and may be…challenging to resolve. You probably need a text editor that’s smart enough to use either a plain text encoding or UTF-8. Linux can usually deal with various Windows encoded files, but I’m not sure we can gracefully/safely handle it automatically.