You can download a copy of the FREE Acrobat Reader for PDF files from HERE
The music can be heard if you have the Sibelius Scorch plug-in. You can download it FREE from HERE.
NB: SlimBrowser will play Scorch files (not all Browsers do) and can be downloaded FREE from HERE
For iPad users, there is now a Scorch App which enables you to hear the music and to amplify individual parts; more information HERE.