Once you know the original font, you can install it on your system if you have a license, or replace it with a similar one.
Since you cannot download these "fonts," you must use one of these workarounds to make the text readable: Embed a font issue in PDF Adobe Acrobat
Since you cannot download these "fonts," you must use one of the following methods to restore the text: Impossible fonts to be found / Fontes impossíveis de achar
The terms in the context of CID (Character Identifier) fonts are usually not specific font names, but rather internal font aliases or "mapping tags" found within PDF documents.