Once you know for sure that it is the correct file format (which it probably is), then you can either convert them all to a common format manually using the trial software, or download some software that will read through a folder and convert them for you automatically.
I'm not exactly what software will let you do this, but the following software is a good place to start:
To change a *.psf file to something readable like a *.jpg, go to "XnView.com" and download the free converter, which changes a .psf file to a .jpg or other usable file format.
Also does batch converting. It's also available on CNET, and has good reviews. I've used it and it works well and quickly.