There is no trial version of Windows 10 Pro, there is a 90 day Enterprise trial you can sign up for an download from the following link:
Try Windows 10 Enterprise | Trial, Download & Evaluation - Microsoft
https://www.microsoft.com/en-us/windowsforbusin..
You can download Windows 10 Pro and use it without a product key if you want.
Download the Media Creation Tool Now
http://go.microsoft.com/fwlink/?LinkId=691209
Right click the MediaCreationTool.exe file then click Run as administrator.
Accept the End User License Agreement:
Select the option Upgrade this PC now if you want to upgrade right away,
Select the option Create installation media for another PC if you want to download a ISO image or create a bootable DVD or USB thumb drive,
Click Next
If you want to download a particular edition or both architectures, uncheck the Use the recommended option for this PC.
Image
Click in the Edition list box, choose your edition then click Next.
Windows 10 - contains Windows 10 Home and Windows 10 Pro.
Windows 10 Home Single Language - only select this edition if you are running Windows 10 Single Language, Windows 8 Single Language or Windows 8.1 with Bing.
Windows 10 N - only select this edition if you reside in Europe, it does not contain Windows Media Player. It contains Windows 10 Home N, Windows 10 Pro N.
Please read the following: Fix Windows 10 Media Creation Tool from Defaulting to Home Instead of Pro
Downloading the ISO file
An ISO file is a digital or virtual replica of a physical disc. In order to use an ISO you must burn it to a optical disc. In the case of Windows 10, a blank Dual Layer DVD or an empty USB thumb drive. If you are using Windows 7, you can create the .ISO then burn it using the built in Disc Image utility. If you are running Windows XP or Windows Vista, you can using a third party burning tool such as ImgBurn or Roxio/Nero.
Creating a .ISO file
For the purposes of this exercise, we are gonna use the .ISO option.
Select ISO file, then click Save, Select your location then click Save.
Wait while the .ISO image is created.
Create a bootable copy from the ISO:
https://answers.microsoft.com/en-us/windows/wik..
How to install it without a key:
Review the following guide for instructions and details about configuring your BIOS or UEFI boot settings for DVD, CD, USB or SD Card.
BIOS/UEFI Setup Guide: Boot from a CD, DVD, USB Drive or SD Card
https://www.groovypost.com/howto/bios-uefi-setu..
Once your computer is set to boot from the DVD, you should see this option. If you are installing from a retail Windows 10 USB thumb drive, you will be asked to select either 32 or 64 bit Windows 10. Learn more here https://www.groovypost.com/howto/choose-windows..
The Windows logo will appear on screen, this might be here for a while, as long as you see the animating dots, everything should be ok.
Select your Language, Time and Keyboard method then click Next.
Click Install now
Windows 10 setup will prompt you for a product key during installation a couple times. If you originally upgraded from Windows 7 or Windows 8/8.1 click the option 'I don't have a key' and 'Do this later' . If you have a Windows 10 product key, you can proceed to enter it.
Setup will also prompt you to select the edition you have a license for - Home or Pro. Please make sure you choose the right edition. If you choose the wrong edition, your only option will be to perform a clean install again.