Hi Djulia,
Sorry to hear you're having trouble!
I'm not sure how much we can do to help with this, but I did a little research. Someone on the [url http://code.google.com/p/wkhtmltopdf/wiki/static]wkhtmltopdf static troubleshooting page[/url] claims to have fixed their font issues by installing the a2ps package. Can you try installing that package on your server or ask your web host to install it for you?
Do any fonts show up in the output at all? You could try out the createPDF_fromUrl() function on a font test page (e.g. [url http://www.electricearl.com/fonttest.html]http://www.electricearl.com/fonttest.html[/url]) to see if some work. If some fonts work, you might be able to supply those as fallback fonts in your CSS — of course, this assumes that you are designing the content you want converted to PDF.
Please let me know how it goes or if you have any questions.
All the best,
Chris