The CD is free, only the product key is what you pay for.

So you could go to www.microsoftstore.com and buy a download version of Windows 8.1.  You'll get an email with the product key, which you can use, and you can just ignore (never download) the actual file.

Answer from @CmdrKeene on learn.microsoft.com
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Fastestkey
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Discussions

Product key needed to activate Windows on 8.1 CD
If you don't need activation, use the below default key: GCRJD-8NW9H-F2CDX-CCM8D-9D6T9 It's for the Pro edition. More on reddit.com
🌐 r/pcmasterrace
6
0
April 6, 2024
Help with 8.1 pro activation key
Use this code: XHQ8N-C3MCJ-RQXB6-WCHYG-C9WKB You need to have a valid product key, as this one would just let you install it. More on reddit.com
🌐 r/windows8
3
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August 27, 2024
Updating to Windows 8.1 for free?
Someone correct me if I am wrong but I believe windows 8.1 will always ask you for a product key during installation and it’s unskippable normally. If you know the original product key for this laptop’s windows installation try entering that and see if it will let you past. Edit: If you have any questions please ask. There are other methods that I didn’t mention here yet that I will bring up if the above doesn’t work out for you. More on reddit.com
🌐 r/windows8
8
5
July 9, 2023
(free) Microsoft 8.1 Pro product key
Please remember that all comments must be civil and helpful toward finding an answer. Jokes and unhelpful responses will earn you a ban, even on the first instance. If you see any comments that violate this rule, please report them. u/ArmadilloDays , check your inbox for a message on how to activate your post. You post will not be visible until you do so. If you do not see an inbox message, here are instructions . Remember to reply Found! to the comment that gave the answer. If looking for an item to purchase, do not click on links sent to you in private messages, and report such to the moderators. I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns. More on reddit.com
🌐 r/HelpMeFind
2
2
January 17, 2023
People also ask

Can Windows 8.1 Professional be installed on modern hardware?
Yes, it can be installed on modern hardware, but compatibility issues with drivers or devices may arise. For a smooth installation, it is advisable to check the availability of drivers on the manufacturer's website.
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mrkeyshop.com
mrkeyshop.com › home › perpetual windows operating system licences and product key › windows 8 licenses › microsoft windows 8.1 professional 32/64 bit - product key
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What is Windows 8.1 Professional?
Windows 8.1 Professional is an advanced version of the Microsoft operating system, designed for professionals and businesses. It offers additional features compared to the standard version, such as support for corporate domains, data encryption with BitLocker, and virtualisation tools.
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mrkeyshop.com
mrkeyshop.com › home › perpetual windows operating system licences and product key › windows 8 licenses › microsoft windows 8.1 professional 32/64 bit - product key
Microsoft Windows 8.1 Professional 32/64 Bit - Product Key
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mrkeyshop.com
mrkeyshop.com › home › perpetual windows operating system licences and product key › windows 8 licenses › microsoft windows 8.1 professional 32/64 bit - product key
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mrkeyshop.com › home › perpetual windows operating system licences and product key › windows 8 licenses › microsoft windows 8.1 professional 32/64 bit - product key
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Tech Resourcia
techresourcia.com › home › blog › windows 8.1 product key and how to activate it
Windows 8.1 Product Key and How to Activate it | Tech Resourcia
December 31, 2025 - If someone buys a copy of Windows 8.1 online with Windows 8.1 Product Key Finder, then they would get the product key online via the email they used for placing their order.
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Electronic First
electronicfirst.com › windows-8.1-pro
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Mr Key Shop
mrkeyshop.com › home › perpetual windows operating system licences and product key › windows 8 licenses
Windows 8 Operating Systems | Microsoft Originals
If prompted, enter the activation code provided by Mr Key Shop to complete the installation and activation of your new Windows 8.1 operating system. If you were not asked to enter the activation code during installation, after completing the ...
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keysincaves
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MS.Codes
ms.codes › blogs › windows › how-to-get-a-product-key-for-windows-8-1
How To Get A Product Key For Windows 8.1
February 29, 2024 - If you're looking to get a product key for Windows 8.1, follow these steps: Visit the official Microsoft website. Navigate to the Windows 8.1 product page. Click on the "Buy Now" button.
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Trulyoffice
trulyoffice.com › blogs › truly-top-picks › free-windows-8-product-keys
Free Working Windows 8/8.1 Product Keys 2024 | Truly Office
February 7, 2024 - Using an illegitimate key can also affect future updates and support for your operating system. Therefore, using a valid and legal product key is always best. Windows 8.1 product keys are not typically free, but you can obtain a free key in certain situations, such as upgrading from an earlier version of Windows.
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SoftwareKeep
softwarekeep.com › blogs › news › free-windows-8-and-8-1-product-keys-that-still-work-in-2021
Free Windows 8 and 8.1 Product Keys That Still Work in 2025
September 4, 2024 - If you want a new Windows 8 or Windows 8.1 product key, purchase from a third-party vendor like SoftwareKeep or Find free Windows 8 and 8.1 Product Keys That Still Work here in this article above.
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Microsoft Support
support.microsoft.com › en-us › windows › activation › find-your-windows-product-key
Find your Windows product key | Microsoft Support
The product key is in the confirmation email you received after buying your digital copy of Windows. Microsoft only keeps a record of product keys if you purchased from the Microsoft online store. You can find out if you purchased from Microsoft in your Microsoft account Order history.