Allows you to check if the fonts in the document were embedded completely or as a subset.
Embedding fonts in a PDF document means that every character of this font is copied and stored in the PDF document. This is useful if you create PDF documents to be displayed on different systems and to be printed on different devices: these are often systems that do not contain exactly the same fonts.
Also, if a font has been completely embedded, you can still edit the text in the PDF file that uses the font in question, even though the font has not been installed on your computer.
Embedding a font as a subset means that only those characters of the font that are actually used in the text are embedded. This reduces the file size by not including superfluous font information. Moreover, you may not want to embed composite fonts completely, because they may contain several thousands of characters and the majority of them will not be used anyway.