How to resolve error code 0x800F081F: .NET Framework 3.5 installation failure during Office 2021 setup

There are multiple ways to address the error code 0x800F081F during the Office 2021 setup. Here are some of the best solutions:

1. Method 1: Manually install .NET Framework 3.5
• Press the Windows key + R to open the Run dialog.
• Type 'appwiz.cpl' and hit Enter to open Programs and Features.
• Select 'Turn Windows features on or off' on the left.
• Check the box for '.NET Framework 3.5 (includes .NET 2.0 and 3.0)' and click OK.
• Follow the prompts to install .NET Framework 3.5.
2. Method 2: Utilize the DISM tool
• Open Command Prompt with admin rights.
• Enter this command and press Enter: DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:X:\sources\sxs(Note: Replace 'X' with the letter of your Windows installation drive.)
• Allow the process to finish and restart your PC.
3. Method 3: Run the Windows Update Troubleshooter
• Open Settings and go to Update & Security.
• Select Troubleshoot from the left menu.
• Click on Windows Update, then Run the troubleshooter.
• Follow the instructions to finish the troubleshooting.
4. Method 4: Temporarily disable antivirus software
• Open your antivirus software and turn it off temporarily.
• Retry installing Office 2021.
• After the installation, re-enable your antivirus software.
5. Method 5: Perform a clean boot
• Press the Windows key + R to open the Run dialog.
• Type 'msconfig' and press Enter to open System Configuration.
• Go to the Services tab and check 'Hide all Microsoft services.'
• Click Disable all, then OK.
• Restart your computer and try the Office 2021 installation again.
• After installation, go back to System Configuration, click Enable all.
• Restart your computer once more.