Welcome to the forums.
What model device do you have? Is the 7100 that your profile shows correct? If you're recieving the PDF as an attachment, you should be able to open and view it with the native attachment viewer. Although it is not always the easiest to see. There are also 3rd party applications such as PDF To Go that will do this for you.
As for the .cda files, they're not supported on BlackBerry devices. You will need to convert them to mp3 files. What kind of ringtones/audio can my Blackberry have? - BlackBerryFAQ