WinConv shoud convert files copied to the hard disk
in some working folder.
Canon Starwriter floppies are plain MS-DOS floppies. You should be able to see the files in the Explorer. If yes, copy the files to the working folder and do the conversion.
Because of the filenaming conventions, it can happen that the files can't be copied to the working folder.
For instance, Canon StarWriter accepts spaces in filenames and accepts upper case and lower case characters. The solution is then to use a disk editor and to correct the culprit filenames.
It can also happen that the Explorer doesn't see anything. If this is a HD floppy, try to mask the second hole (the one without read-only slider) and try again.
The floppy drive of the processor could namely format a HD floppy as a logical DD one.