This topic is quite old, but here is a handy solution that I found:
http://www.cityinthesky.co.uk/opensource/pdf2svg/
It offers a tool, pdf2png, which once installed does exactly the job in command line. I've tested it with irreproachable results so far, including with bitmaps.
EDIT : My mistake, this tool also converts letters to paths, so it does not address the initial question. However it does a good job anyway, and can be useful to anyone who does not intend to modify the code in the svg file, so I'll leave the post.