Originally Posted by porkupan
The CRAMFS filesystem images cannot be edited "on the fly". They must be regenerated on another computer. I hope you realize this before you start messing with those fonts. Yes, the fonts filesystem can be reflashed, but you need to know what you are doing first.
Thanks for your answer.
My another question is that why in epub the font path "res:///mnt/sdcard/fonts/fontname.ttf" doesn't work. Does "res://" point to another place?