Codes to unlock v4.x (& 5.x):
The officially free code presented by author for v5.9.5 also unlocks v4.x it is
Name> GraphicConverter User <-- (any, or your own name is OK)
Code> GC99-FZAFSK-PUU

other codes tested both 4.x & 5.x :
Name> any
Code> GC99-PZKKDA-NTY
or GC99-DDJAFF-PPU
or GC99-DZKKAR-CCP
or GC99-PPKDKD-WBT