Fonts embedded inside PDFs are intended for use inside PDFs only. In some cases just extracting a font in a PDF might give you a font that also works outside the PDF, but that is coincidental.
If you wish to understand, why, polease read the font sections in the PDF standard (ISO 32000-1) as well as the applicable font format specifcations, or at least the TrueType specification and the PostScript Type 1 font specification, and related specifications (you will find all the pointers to these document in teh PDF standard, either under NMormative References or under Bibliography).
Olaf