I have Sound Forge on my Windows OS. It won't load onto my IMac 27, saying my Sound Forge version is only for Windows. Do I have to purchase Sound Forge specifically for IMac?
Sound Forge for MAC was discontinued some years ago by Magix, so there is no version for your iMac, sorry.
You might be able to install and run it on your Mac if you are prepared to create a separate partition on your hard drive and then install Parallels, or similar, followed by a Windows version on that partition. Sound Forge should then install on this Parallels/Windows partition but there is a real possibility that it will not run successfully!