PDAs, particularly WindowsMobile and select Android models, offer voice activation capabilities, though none compare to the voice activation and dictation capabilities offered by Windows Vista/7 and/or the third-party Dragon Naturally Speaking. That makes a tablet PC the better option, but does not rule out a PDA.
As to Microsoft Office, WindowsMobile PDAs come with a mobile version installed, though it is dramatically drilled down to the key functionality. All other major mobile operating systems, with the exception of WebOS, currently support Documents To Go by Dataviz, a third-party suite with similar, but slightly more enhanced, capabilities. Depending what the user intends to do with Office, though, that may rule out the mobile versions, necessitating a tablet PC.
Camera and file syncing are both nearly universal, making voice recognition and Office the top considerations. You'll also want to determine the user's price range, as PDAs (usually $200-$600) run significantly less than tablet PCs (usually $1200-$3000).
Let us know which would be best given the circumstances and we can make some recommendations.