Originally Posted by grannyGrumpy
Please give details of how this is done. Thanks.
What I do is take the finished ePub, load it into Calibre, convert to ePub using subsetting and then I take the font directory out of the converted ePub, replace the font directory in the finished ePub, fix the CSS/OPF as needed to match the fonts and done. Now I have an much smaller ePub with subsetted fonts. Also, don't forget to validate the finale finished ePub (I use FlightCrew) to make sure I didn't make a mistake editing the CSS/OPF (if I have to edit them).