If the version downloaded from Softonic is an authorized download, you still have to have your own valid license key to install the software. Personally, I wouldn't trust it from Softonic but instead would go direct to DigitalRiver.com
If your computer as a functioning factory restore image or if you made the factory restore disks, then a license key is part of the image. Your computer has one specifically assigned to it and it is on the Windows COA sticker on the machine, but most people just use the one which came in the image - all the machines from that mfg have the same license shipped out the door.
Failing that, you will either have to purchase one or you could try your luck crying on the shoulder of a MicroSmurf, but I doubt you would have any success there.