Please i want to ask about the ability to extract embedded fonts from pdf is easy or not? because i tried to extract fonts form specific pdfs but there are fonts that not valid files, why these files not valid? are there specific technique to extract fonts from pdf?
Fonts inside a PDF aren't required to be "OS installable" fonts – in fact the vast majority (>90%) will not be, as most of the information that isn't needed by PDF (but would be to use the font in other environments) has been removed to save space.
Each font has its own licensing terms. Certainly, if you extract fonts from PDF files and install them in the local system, it will often break those license terms.
Many fonts have "embedding licenses". These allow you to own a font, and embed it in a PDF, to be viewed on other systems; the same license doesn't allow it to be shared with other systems for any other use.
So, since extracting the fonts would often break the license, the best advice is: if you want to use the same font as found in a PDF, just buy it... and hope it will be recognised as the same font, because it often is not.
Ok thanks test screen name for continous help, I want ask about another thing, there are tools such as pdfextract and other online tools that extract fonts from pdf, can i work with these fonts or not?
Technically: don't know. If they just extract the font streams unmodified, unlikely to be of much use. Most fonts are subset so they are no use.
Legally: check the font license. Yes, each single individual font has a different license. The easiest way to avoid issues and endless checking is to not think about using them from a PDF.