fotomagico purchase

I now have fotomagico 3. If I was to purchase FM 4 from the mac app store, would I still be able to use 3 or would 4 replace the 3 I already have?

I would suggest renaming FotoMagico 3 you already have installed to “FotoMagico 3” in your Applications Folder. Since FotoMagico 4 will also just be named “FotoMagico” this will not overwrite the old install. You can use them side by side if you want