How do I embed fonts in a PDF?

Hi,

I generated my PDF book with docbook and tried to upload it to lulu.com.
Lulu.com reject my upload stating that ...


Your document could not be created: This font is not embedded:
Helvetica-Bold ( How do I embed fonts?) This font is not embedded:
Helvetica ( How do I embed fonts?)
This font is not embedded: Times-Roman ( How do I embed fonts?)

... what are they talking about and what can I do in my custom style
sheet to fix it?

Thank you.