Hello...apologies for the delayed reply...hopefully you already received an answer elsewhere, but just in case...
PDF's can be opened natively on any BB for as long as the PDF is an email attachment. Once detached from an email, the BIS service is no longer present to render the file, and a 3rd party app would be required to render it on the device. epubs would definitely require some 3rd party app to render them.
Your best bet is to search AppWorld and perhaps use Google to find the various options for your needs, and then select the one that most closely matches.
Occam's Razor nearly always applies when troubleshooting technology issues!
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