Create a TrueType font out of a OpenType one (e.g. because OpenOffice.org and VISIO doesn’t support .otf) by using FontForge:

otf2ttf

#!/usr/local/bin/fontforge
# Quick and dirty hack: converts a font to truetype (.ttf)
Print("Opening "+$1);
Open($1);
Print("Saving "+$1:r+".ttf");
Generate($1:r+".ttf");
Quit(0); 

Save the script as otf2ttf and type:

  fontforge -script otf2ttf FONTNAME.otf 

If you want to convert many .otf fonts in a directory to .ttf fonts, type (thanks sw!):

  for i in *.otf; do fontforge -script otf2ttf $i; done 

Ref: http://www.stuermer.ch/blog/convert-otf-to-ttf-font-on-ubuntu.html