pfi to pdf conversion can actually mean several things as many different file types use pfi file extension. As a rule, any graphics or documents file can be exported to PDF format either with dedicated PDF export function or with a virtual PDF printer. Examples of this would be export of Panorama Factory graphics files or PhotoFilter Studio files.
Open PFI file Open PDF file
A complete image retouching program
A photo editor used to create panorama pictures
A picture editing software for Mac