How do I embed fonts using the Adobe XI please?

If you have Adobe Acrobat XI Professional (not Standard) you can embed fonts available on your system using Preflight tool and Embed Fonts profile under PDF fixups.
To do this go to menu View -> Tools -> Print Production, choose "Preflight" and under "PDF fixups" click on "Embed fonts" profile:

Note: Not all fonts are embeddable.

Do note that the computer you are using to run the Acrobat Pro Preflight (Preflights are not available in Standard or Reader) has to have the fonts available on the computer system.

Often easier is to configure a default Distiller Job Option that embeds fonts. When mastering content in the authoring file always use plain brown paper bag kinds of fonts then output to PDF via PDFMaker or the Adobe PDF virtual printer using the Job Option. Having it as part of the core work flow means one less "post-processing" activity.

Be well...