The output of pdv will depend on the contents of your archive. You can see what state is your data in with the following command:
psredit -c state.fits
If the answer is not "Stokes", then in order to return I, Q, U and V you need to convert your data to Stokes state. If you want to keep your archive just like it is without making any changes you could run:
pdv -j 'state Stokes' -t file.fits > new.dat
Hope this helps.