This simple guide will walk you through the steps to download and install Windows 10 on your Mac Pro. And how to install and use Boot Camp so you can switch between Windows 10 and macOS X. Windows 10 will be installed on it’s own drive in one of the SATA drive bays. A Mac graphics card is not necessary.
For the install you will need: A hard drive or SSD for Windows. A blank Dual Layer DVD. A USB Flash drive, or external USB Drive, 4GB or larger.
Both drives must be erased and formatted as Master Boot Record & MS-DOS (FAT).
NB Boot Camp Assistant is not compatible with Mojave and the Mac Pro. You must use High Sierra or earlier to create the Boot Camp USB installer.

Download the latest 64 bit version of Windows 10 from Microsoft. https://www.microsoft.com/en-us/software-download/windows10ISO
Select a Version and click Confirm, select a Language and click Confirm, then click 64 Bit Download and the download will start.
When the download has completed open the Terminal app. Applications > Utilities > Terminal.
Type the following command in the window, replacing macuser for the name of your home/user folder etc. and hit return. (*1-1)
drutil -drive 1 burn /Users/macuser/Downloads/Win10_1909_English_x64.iso
If you have two optical drives installed you can replace -drive 1 with -drive 2 to use the upper drive.
If the command is typed correctly, and the file name and path are correct, the DVD/Optical drive tray will open.
Place the blank DL DVD in the tray and gently push it to close.
Terminal will automatically start burning the Windows Installer to the DVD.
When the disc has finished burning it will eject. Confirm the Terminal window states Burn Completed. (*1-2)
Quit the Terminal app, Gently push the tray to close leaving the Windows Installer DVD in the drive.
Now insert your USB drive and open Applications > Utilities > Boot Camp Assistant (Works with OS X 10.13 or earlier only).
When Boot Camp Assistant opens click Continue.
Only select the checkbox for ‘Download the latest Windows support software from Apple’ and then click Continue.
Check the destination disc listed is the correct location, and click Continue.
Boot Camp Assistant will download and copy the Boot Camp files to your USB drive.
You will be prompted for a password. Enter your password and click OK.
When Boot Camp Assistant has completed the USB installer click Quit.
Now shut down your Mac Pro. You should still have the Windows 10 disc you burned in the DVD / optical drive.

If your computer has shut down, remove the USB drive, and all other types of storage and hard drives, apart from the SATA drive you will use for Windows. You can leave the hard drive or SSD you will be using as the Windows drive in any SATA slot.

Start up the computer and hold the C key on the keyboard until you see the Windows logo to start up from the Windows DVD.
You will see only the blue Windows icon for some time.
When the installer has loaded, select a language etc and click Next.
Select Install now.
Enter a product Key and click Next / Or click 'I don't have a product key'- then select 'Windows 10 Pro' and click Next.
Accept the license and click Next. There is a Free 90 day trial period and/or you can buy a product license key for a few $'s.
Select Custom: Install Windows only (advanced).
On the following 'Where do you want to install Windows' page, first click Format, click OK in the popup window, and then click Next.
The Windows installation will start.
The computer will reboot twice during the installation.
When the installation has completed, follow the prompts and enter the necessary info to set up Windows.
When you reach the Windows 10 desktop, click on File Explorer from the menu bar.
In the window that opens click on This PC.
Right click the DVD drive icon and select Eject.
Remove the Windows install DVD from the drive and gently push it to close.
Now click on the Windows icon in the bottom corner / Start menu and click on Settings.
Click on Update & Security.
Click on Check for Updates.
Allow the downloads to complete and install. This may take a while.
When the updates have completed you will be prompted to restart the computer.
Click Restart now, Windows will install the updates and reboot.

Now insert the USB drive with the Boot Camp files you set up earlier.
Click on File Explorer in the menu bar, and select the Boot Camp folder on the left side of the window.
Find the file called 'setup' and double click it to start the Boot Camp installer.
Click Yes in the popup window.
Click Next in the Boot Camp Installer window.
Accept the terms of the license agreement and click Install.
The installer seems to hang and takes some time to complete.
Click Finish when Boot Camp Assistant has finished installing.
Click Yes in the popup window to restart the computer.
After the computer reboots another installer might start. If so, allow the installation to complete.
Then shut down the computer.

When Windows has shut down, remove the Boot Camp USB installer and replace any drives you previously removed back into your computer.
Start the computer, if you have a drive with OS X installed it will boot into OS X, otherwise it will boot back into Windows.
When the computer has booted into Mac OS X, open System Preferences > Startup Disk.
Click the lock and enter your password in the popup window.
Select BOOTCAMP as the startup disk, click Restart, and click Restart again in the popup window.
The computer will reboot to Windows.
When booted to Windows Click the up arrow ^ on the right side of the menu bar.
Click the Boot Camp icon/ black diamond from the hidden tools.
Click ‘Restart in OS X, and click OK in the popup window.
Your computer will shut down and reboot into OS X
You should now be sure you can boot between OS X and Windows, using Boot Camp in Windows, and Startup Disk in OS X.
You’re all done!

If after the install has completed you have any problems with booting correctly, you should shut down the computer, reboot and reset the PRAM. Your computer should then reboot to OS X. Go to System Preferences > Startup Disk, select the desired startup disk and restart the computer.
The Boot Camp Control Panel in Windows does not show/see a drive formatted with the APFS file system that High Sierra, Mojave and Catalina use. But if you select Reboot in OS X from the menu bar tool your Mac Pro will reboot into OS X.
1-1) If the file you downloaded from Microsoft in Step 1 is named something different than is shown (Win10_1909_English_x64.iso) then you must change the file name you enter in the Terminal window. Also, if your web browser saves files to a location other than the default Downloads folder you will have to change the file path accordingly.
1-2) If the disk burn fails you will have to re-type the terminal command, insert a fresh DL DVD disk, and start the disk burn again.