There should already be a reader loaded. most times you need to save the file then open it. There is a freeware/shareware program "filescout" that helps you navigate your files or you can use the Media player and "explore from the program's first window. Navigate to the saved file and click to open.
Sometimes attachments in emails need to be saved before you can open them.
Link to BBfilescout:
http://www.emacberry.com/ota/BBFileScout.jad
Link to PDF reader if missing from phone: for curve...
http://www.downloadatoz.com/toplight...df+reader.html