The Blackberry browser can open .pdf files but not stand-alone .pdf files. You will need a stand alone app to open .pdf files. I keep hoping one day Adobe will make a free version for Blackberry, but I don't think it will happen. I purchased the Premium version of Docs to Go, which comes on every Blackberry in the free version. The Premium version includes a .pdf reader, which works great. There are other .pdf readers out there, you just have to look. One place to look is on Blackberry App World. Hope that helps.
For us really cheapo's the work around is to email the pdf to yourself so you can read it then delete the email. When I open my wallet I have to blow the dust out to see if there are any dollars in it.