I have not tried Windows 8.1 Pro yet but decided to give it a try for my new water cooled PC. The new PC has no optical drive so I needed to create USB flash install media. Here are the steps I took to create appropriate media using Windows 7. Once you use the media to install you will need a product key.
Windows 8.1 Pro Media Creation Steps
This will save a file to your PC. Open/Run the resulting file – mine was called mediacreationtool.exe. Accept any security warnings and you will get a purple install window. I selected the following options and clicked Next.
The next screen looks like this. Make sure the USB flash drive option is selected and click Next.
On the resulting screen select the flash drive you wish to use and click Next. For me this drive was K:
You will probably get a message warning you that the files on the drive will be deleted. If you are ok with that, press OK. A downloading screen will appear and give you an idea of how long the process will take. For me the process took about 10 minutes. After the download, the installer will check the files and go through a process it calls getting the files ready. Finally it will go through a process called Creating the USB Flash Drive. All of these steps happen on the same screen and take another 5 minutes or so with no interaction required.
The final screen looks like this. All that is left to do is click Finish. That is the end of the process.
Creating Windows 8.1 Pro media on a USB flash drive is a simple process that takes about 15 minutes from start to finish. I find this preferable to using a DVD to install and will use the process again in the future.