How to install Microsoft Office 2021 Professional Plus
This guide explains how to install Microsoft Office 2021 Professional Plus on a Windows desktop or laptop using the installation method supplied by EcoKeys.
The process is straightforward, but it is important to remove conflicting Office installations first and to check that Office has actually activated when the installation is complete.
Installation overview: Remove old or conflicting Office versions → download the Microsoft Office 2021 Professional Plus installation file → open the downloaded image → run Setup → allow Office to finish installing → restart the PC → open Word → enter your supplied product key → confirm activation in File → Account.
Office 2021 lifecycle notice: Microsoft support for Office 2021 ends on 13 October 2026. Existing installations may continue to work after this date, but Microsoft will no longer provide Office 2021 security updates, bug fixes or normal technical support.
This installation guide remains available for customers who already have a valid Office 2021 Professional Plus licence.
Before You Install Office 2021 Professional Plus
Taking a few minutes to check the PC before installation can prevent many of the most common Office setup and activation problems.
Have your product key ready
Your Office 2021 Professional Plus product key is supplied in your EcoKeys order email. Keep the email available while completing the installation.
Use a stable internet connection
The Office installation image is several gigabytes in size, so allow enough time for it to download fully before trying to open it.
Remove conflicting Office versions
Older Office installations and Microsoft 365 trials can cause the wrong edition to open or interfere with activation.
Do not interrupt the installation
Once Setup begins, allow it to finish completely before restarting or shutting down the computer.
Step 1: Remove Previous or Conflicting Office Versions
Before installing Office 2021 Professional Plus, we recommend removing previous Microsoft Office installations that could conflict with the new installation.
This is especially important if the computer already has:
- Microsoft 365.
- An Office or Microsoft 365 trial.
- Office 2016, 2019, 2021 or another Office edition you no longer require.
- A different Office Professional, Home & Student or Home & Business installation.
- A partially installed or failed Office installation.
Already removed your previous Office installation? You can move directly to Step 2.
For the current removal methods, follow our dedicated guide:
Watch for the pre-installed Microsoft 365 app
Many new Windows PCs include Microsoft 365 apps or shortcuts before you install your purchased Office version.
Do not assume that opening the first Word or Office icon you see after installation means you are opening Office 2021 Professional Plus.
Later in this guide we will show you how to check the installed edition in Word → File → Account.
Step 2: Download Microsoft Office 2021 Professional Plus
Use the Microsoft download below for the Office 2021 Professional Plus installation used in this guide.
The download comes from Microsoft's Office CDN. The file name should be ProPlus2021Retail.img.
Your browser should begin downloading the file to the computer's normal Downloads folder unless you have configured a different download location.
The file is large, so the time required depends on your broadband connection and current Microsoft server load.
Do not try to open a partially downloaded file. Allow the browser to show that the download has completed before continuing.
Browser security messages
A browser may occasionally ask you to confirm that you want to keep a disk-image file because the .img file type is less commonly downloaded than a normal document.
Check that the download is coming from the Microsoft officecdn.microsoft.com address shown above before proceeding.
Do not download an Office installer from an unknown mirror or third-party download website simply because your browser displays a warning about the file type.
Step 3: Open the Downloaded IMG File
When the download has completed:
- Open File Explorer.
- Open your Downloads folder.
- Find ProPlus2021Retail.img.
- Double-click the file.
Windows should open or mount the disk-image file and display the Office installation files.
If double-clicking the IMG file does not open it
- Right-click ProPlus2021Retail.img.
- Select Mount if the option is available.
- Open the newly mounted Office drive shown in File Explorer.
The mounted image behaves like a temporary DVD drive. This is normal and does not mean Office has been installed yet.
Step 4: Run Office Setup
Inside the mounted Office installation image, locate the Setup application.
- Double-click Setup.
- If Windows asks whether you want to allow the application to make changes to the device, select Yes.
- Office installation will begin.
- Leave the computer switched on and allow the process to complete.
Do not restart the computer while Office is installing. Wait until Office confirms that the installation has completed.
The exact installation time varies between computers. Allow the process to finish even if the progress appears to pause for a short period.
When installation completes
- Select Close.
- Close any remaining installation windows.
- Restart your desktop or laptop.
Step 5: Find the Correct Office 2021 Applications
After Windows restarts, open one of the newly installed Office applications.
- Select the Windows Start button.
- Type Word into Windows Search.
- Open Microsoft Word.
Do not simply open an old “Office” or Microsoft 365 shortcut. A computer can contain shortcuts or applications from a previous Microsoft 365 installation even after Office 2021 has been installed.
Confirm you are opening Office 2021 Professional Plus
In Word:
- Select File.
- Select Account.
- Look under Product Information.
If the Product Information area shows a completely different Office edition or Microsoft 365 installation, stop before activating.
Return to the removal guide, remove the conflicting Office installation and then repeat the Office 2021 installation.
Step 6: Activate Office 2021 Professional Plus
If Office displays the product-key activation screen:
- Copy the 25-character Office 2021 Professional Plus product key from your EcoKeys order email.
- Paste or type the key into the activation box.
- Check the characters carefully.
- Continue through the on-screen activation prompts.
- Keep the computer connected to the internet while Office verifies the licence.
Copy and paste the key where possible. This avoids confusing similar-looking characters when entering a 25-character product key manually.
If no product-key screen appears
Do not assume Office is activated simply because Word opens normally.
Open:
Word → File → Account
Under Product Information, check the activation status.
If Office is not activated and the option is shown, choose Change Licence, Change Product Key, Switch Licence or the equivalent product-key option shown by your Office build, then enter the product key supplied in your order email.
IMPORTANT — Check Your Office 2021 Activation
Do not skip this step
Office can sometimes open before you have confirmed that the product is fully activated. A grace period or previous Office licensing information can make an installation appear complete when activation still needs attention.
- Open Microsoft Word.
- Select File.
- Select Account.
- Look under Product Information.
- Confirm that Office shows as activated.
If Office still asks you to activate, shows an unlicensed-product message or displays a licensing error, do not repeatedly reinstall Office. Use the support section below.
Installed
The Office applications have been copied to the PC and Word, Excel and the other included programs can open.
Activated
Office has accepted the valid licence information and the installed product reports that activation has completed.
Common Office 2021 Installation Problems
The IMG file will not open
Right-click ProPlus2021Retail.img and choose Mount. Open the mounted Office drive and run Setup.
Setup will not start
Restart Windows and check that another Office installation is not already running. Also confirm that the complete IMG file has downloaded.
Word opens but shows Microsoft 365
Check Word → File → Account. If the wrong Office product is listed, remove the conflicting installation before repeating the Office 2021 setup.
I installed Office but cannot find Word
Select Start and search specifically for Word. Do not rely on a generic “Office” shortcut.
Office asks me to activate
Enter the Office 2021 Professional Plus key from your order email and then verify activation under File → Account.
The product key gives an error
- Confirm Office 2021 Professional Plus is installed.
- Check the product key was copied correctly.
- Check the PC is connected to the internet.
- Check that another Office or Microsoft 365 installation is not interfering.
If the error remains, use EcoKeys Rapid Support.
Office worked but now shows Unlicensed Product
Open Word → File → Account and note exactly what is shown under Product Information. Then use Rapid Support and provide the requested screenshots.
Office 2021 Reaches End of Support in October 2026
Microsoft support for Office 2021 ends on 13 October 2026.
After this date Office 2021 will no longer receive:
- Security fixes.
- Bug fixes.
- Office 2021 software updates.
- Normal Microsoft technical support.
If you already own Office 2021, this does not prevent you installing and activating your valid product today. It does mean you should be aware of the upcoming Microsoft lifecycle deadline.
See our Office 2024 vs Office 2021 comparison for more information.
Having an Installation or Activation Issue?
Use EcoKeys Rapid Support
For the quickest response, use the EcoKeys Rapid Support portal rather than trying random fixes from forums or repeatedly reinstalling Office.
The portal will guide you through the information and screenshots needed to diagnose the problem correctly.
Response target: within 30 minutes during published support hours.
Before contacting support: Open Word → File → Account and be ready to provide a screenshot of the Product Information area together with the exact activation error shown.
Office 2021 Installation Checklist
Remove conflicting Office versions
Including Microsoft 365 trials or previous Office installations where required.
Download ProPlus2021Retail.img
Use the Microsoft Office CDN link in this guide.
Open or mount the image
Windows can normally mount the IMG file without additional software.
Run Setup
Allow Office to finish completely before restarting.
Restart Windows
Then search for and open Microsoft Word.
Check the installed edition
Word → File → Account.
Enter your supplied product key
Follow the activation prompts shown by Office.
Confirm activation
Do not finish until File → Account shows Office as activated.
Related Office Guides
Frequently Asked Questions
Should I uninstall Microsoft 365 before installing Office 2021 Professional Plus?
If Microsoft 365 or another Office installation could conflict with Office 2021, remove it first.
Where do I download Office 2021 Professional Plus?
This guide uses Microsoft's Office CDN download for ProPlus2021Retail.img.
How do I open the Office 2021 IMG file?
Double-click it. If Windows does not open it automatically, right-click the file and select Mount.
How do I activate Office 2021 Professional Plus?
Open Word and enter the 25-character product key supplied in your EcoKeys order email. Then check File → Account.
What if Office does not ask for my product key?
Open Word → File → Account and use the available Change Licence, Change Product Key or equivalent option.
How do I know Office has activated?
Open Word and check File → Account → Product Information.
Why does Word still show Microsoft 365?
A previous Microsoft 365 installation may still be present. Check File → Account and remove conflicting Office installations if necessary.
Should I reinstall Office repeatedly if activation fails?
No. Check the installed product and exact activation error, then use EcoKeys Rapid Support.
When does Office 2021 support end?
Microsoft support for Office 2021 ends on 13 October 2026.
