The vst Synthfont has a DLL file that is usually placed where the other vst's are placed or in the synthfont folder.
You need to find this Synthfont.DLL when you go to add VST. This will link the synthfont to the list of other vst's like Virtual sound canvas VSC in the list of vst's you can choose from. When you do this you can choose which one you wish to use. You also need to have a GM soundfont group to use within the synthfont program.
I down loaded the Fluidr3.sf2 which is a compressed file on the synthfont webpage. download the SFARK program to unpack the soundfonts and it will have a sf2 extention after unpacking.
I had a bit of a problem unpacking the sfark file till I did a left mouse click on the file and chose "open with" sfark and it went smoothly
Hope this helps. Wyndham