I see a Deskjet F4180 but not a Deskjet F1480 at the HP support site. Normally you just use the software to bridge to OCR. No need to set a file extension. You just send the scanned document to Word.
Are you sure you have the OCR software installed? This from HP:
If you are using HP Photosmart Essential, the Optical Character Recognition (OCR) software might not be installed on your computer. To install the OCR software, you must re-insert the software disk and select OCR under the Custom installation options.