As Faltradl said, if the fonts are not on your personal computer, they cannot be embedded.
However, I wanted to add that font names are not used definitively. While commercial typographic font makers try to come up with a unique name that could be trademarked if their product is wildly popular, most knock-off and hobby font makers do not.
Commercial fonts generally include a larger selection of glyphs/characters than most free fonts offered. Another difference is the usage rights; many free fonts are for "personal use" and cannot be used in/for commercial products. So embedding the font for anything other than your own use can be an issue.
So, for example, the font Times New Roman (one of the most well know and used fonts in western publishing), there can be wildly different appearances between the same letters over several different maker's interpretations and skills at font crafting & hinting. In other words, you could download 20 versions of Times New Roman and get 20 different fonts. Admittedly, most of these variations will be minor and quite possibly will not appear except at larger font sizes (20 points and up), but sooner or later the differences will appear - particularly in accented letters or ligatures.
So even if you:
- search the internet,
- find a comparably named font,
- install it on your computer, and
- then embed the font into the ebook
you still might not have the same visual appearance as the author/publisher intended because it's not the
exact same font.
The best that you can do is embed an acceptable font, to you, by using the Editor to replace the font references and re-save the ebook.