If you're testing Windows before you buy, you're stuck with an annoying 'Activate Windows' watermark on your desktop. It overlays most applications, which makes it a true pain.

'Activate Windows' Watermark on Deactivated Version of Windows

Here's a quick way you can remove it in 2 simple steps.

Create a text file with the following code.

@echo off
taskkill /F /IM explorer.exe
explorer.exe
exit

Click 'Save As...' and save it as RemoveWatermark.bat.
Make sure your file is saved as a .bat file. If you saved it as a .txt file, you will not be able to execute it. If you're having trouble modifying the file format even when adding the .bat extension, open a File Explorer window, navigate to the View tab, and ensure the checkbox next to File name extensions is checked.
Right click RemoveWatermark.bat and run it as an administrator.
Restart your computer.

Tada! Your watermark is gone. Now you can test your Windows experience without that pesky annoyance.

Note: This is not meant as a workaround to buying Windows. I highly recommend paying for Windows.