So I needed to read a PDF out loud on my iPhone 4 (iOS 5) but the VoiceOver option did not like reading it to me from Acrobat Reader for iPhone or Dropbox 1.4.6 for iPhone. So the workaround I found was to open the PDF from Dropbox, click the export button in the lower right hand corner and choose iBooks. This exports the PDF from DropBox to iBooks. Then all I had to do was turn VoiceOver on under Settings>General> Accessibility>VoiceOver and go back over to the iBooks app and tap the screen. Yay.
Short post, but maybe this will help somebody. BTW, don't forget that you should never use Dropbox for anything confidential in nature as they not only had a gaping security hole not too long ago, but they also didn't even proactively inform their users of the bug that left their files open to the entire world.