You can buy an App called Files and Folders that shows every file on the PlayBook. There is a free time limited trial version available or you can purchase it for $2.99. It is a great app. I have used it for about a year.
Files downloaded via the standard browser or received via e-mail usually end up in this folder:
Files & Folders, the unified file & cloud manager for PlayBook and BB10 with SkyDrive, SugarSync, Box, Dropbox, Google Drive, Google Docs. Free 3-day trial! - Jon Webb - Innovatology - Utrecht, Netherlands