The only 3fr to pdf conversion we know about this time is the export of Hasselblad 3F RAW images (.3fr) to PDF format, probably in an effort to print the picture as a document.
Any graphics file can be exported to PDF format, which puts the picture on one of the pages in the document. Just keep in mind that the resulting file will be huge. Special RAW metadata won't be saved either, just the raw raster or bitmap content.