Some fonts are embedded within a PDF file, while others are not.
If a font is not embedded, BuildVu will use an open source fallback font.
If a font is embedded, BuildVu will write the font out during conversion.
There is no reliable way to tell programmatically what license a font has. Many font licenses pre-date the internet, which means there is no clear answer as to what is or is not allowed.
The responsibility of knowing whether a font can be used is with the user of the font, and we do not offer legal advice on this.
If you would like to avoid outputting the font file, one option is to set BuildVu to use a non-selectable shapetext mode. In this mode, BuildVu will convert the text into shapes (either rasterised to image or output as SVG) and will no longer output the font file. More information on text mode options can be found here.