2 Answers

The only free versions are the copies that are not recognized by Microsoft. You can install it but every time you use your computer, you will get  message that it's not a genuine copy and ask you for a key. The only way to get the key is to buy one from Microsoft. You may as well just spend the money and buy a genuine copy now. 

The first option is to go to a watchmaker and have them demagnetize your watch. While this is a fine choice (and even saves you from reading the rest of this article), access can be difficult in some areas, and let's face it, going to your watchmaker does not a How-To make. For those willing link to roll up their sleeves and push link a single (and exceedingly low effort) button, I link recommend picking up a watch demagnetizing tool.