Portable Fonts not working

After downloading portable apps platfrom to kingston 8gb flash drive, i put a couple of otf and ttf format fonts onto the platfrom's font directory folder inside the Portableapps.com/data/font directory. However, after launching libreoffice from my flash drive, the new fonts did not appear in the fonts list. After a couple of hours, i tried again with no luck. The fonts don't appear on any other programs either. Please tell me how to fix this problem