PSD isn't even proper print format. It's the native editing mode Photoshop format used to create/edit an image and then save to a finished TIFF (or other print) or JPEG (or other web) files. Akin to PNG being the native Fireworks format (and, unfortunately, not the same as that used for actual images.png!
(PSD saves the layers and editing capabilities that you don't want in the finished file. )