How to Download and Enable .NET Framework 3.5 on Windows 10

If an older program asks for .NET Framework 3.5 on Windows 10, you normally should not download a separate legacy installer. On Windows 10, .NET Framework 3.5 is a Windows Feature on Demand. Enable the feature and Windows downloads the required files from Windows Update. If the PC is offline or Windows Update is blocked, use matching Windows 10 installation media as the source.

.NET Framework 3.5 includes support for .NET 2.0 and 3.0 applications, and it can coexist with .NET Framework 4.x. Microsoft also recommends using a newer version of an app when one is available because .NET Framework 3.5 is primarily kept for compatibility with older software. See Microsoft's official .NET Framework 3.5 installation guidance.

Enable .NET Framework 3.5 with Windows Update

This is the simplest method for a Windows 10 PC that can reach Windows Update. Sign in with an administrator account before you begin.

Open Windows Features. Press Start, type Windows Features, and select Turn Windows features on or off.

Windows 10 Start search showing Turn Windows features on or off — Search for Windows Features from Start, then open Turn Windows features on or off.

Select .NET Framework 3.5. Check .NET Framework 3.5 (includes .NET 2.0 and 3.0), then select OK. You do not need the WCF activation subfeatures unless software documentation specifically requires them.

Windows Features dialog with .NET Framework 3.5 selected — Enable the .NET Framework 3.5 parent feature; the WCF activation options are usually unnecessary for desktop apps.

Let Windows get the feature files. If Windows asks how to obtain the required files, choose the option to download them from Windows Update. Keep the PC online until installation finishes.

Windows Features prompt offering to download required files from Windows Update — Windows Update can download the payload required to finish enabling .NET Framework 3.5.

Finish the installation. Close the completion dialog and restart the PC if Windows asks you to. Then launch the program that required .NET Framework 3.5.

Windows Features completion screen after installing an optional feature — A successful installation ends with Windows reporting that the requested changes are complete.

Install .NET Framework 3.5 offline with Windows 10 media

For Windows 10, Microsoft says the supported offline method is to use the feature files from Windows installation media. The old .NET Framework 3.5 SP1 standalone installer is intended for earlier Windows versions, not as the supported offline installer for Windows 10.

Prepare matching Windows 10 media. Mount an ISO or connect installation media that corresponds to the Windows 10 version on the PC. In File Explorer, note its drive letter and confirm that it contains a sources\sxs folder. Microsoft warns against using source files from a different Windows version because a mismatch can fail or leave the system in an unsupported servicing state. If needed, use Microsoft's Windows installation media instructions.

File Explorer showing the sources sxs folder on mounted Windows 10 installation media — The offline source is the sources\sxs folder on matching Windows 10 installation media.

Open an elevated Command Prompt. Search for Command Prompt, right-click it, and choose Run as administrator.
Run DISM with the media as the source. Replace D: with the actual drive letter for your mounted ISO or USB, then run: DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:D:\sources\sxs. The /LimitAccess switch tells DISM not to contact Windows Update.

Administrator Command Prompt with DISM NetFx3 command using D sources sxs — Run the NetFx3 DISM command from an Administrator Command Prompt, using the correct media drive letter.

Confirm that DISM succeeds. Wait for the operation to reach 100 percent and report that it completed successfully. Restart Windows if required by your environment, then try the legacy app again. Microsoft documents the same syntax in its DISM deployment guide for .NET Framework 3.5.

Administrator Command Prompt showing DISM operation completed successfully — A successful DISM installation reports that the feature operation completed successfully.

What to do if .NET Framework 3.5 will not install

Errors such as 0x800F0906, 0x800F081F, and 0x800F0907 usually point to download, source-file, or policy problems. Error 0x800F0922 can also appear during feature installation, although Microsoft notes that it is not specific to .NET Framework.

Windows Features error message with code 0x800F081F for missing required files — Error 0x800F081F commonly means Windows cannot find a valid source for the required feature files.

For 0x800F0906, check whether the PC can reach Windows Update and whether a proxy, firewall, or organization policy blocks the download.
For 0x800F081F, verify the source path and use installation media that matches the installed Windows 10 version.
For 0x800F0907, a Group Policy setting may prevent Windows from downloading optional-component payloads. On a managed PC, ask the administrator rather than changing domain policy yourself.

Microsoft's .NET Framework 3.5 installation error reference lists the causes and approved resolution paths.

Do you need to remove newer .NET versions?

No. Do not uninstall .NET Framework 4.x just to add 3.5. The versions serve different application targets and can exist side by side. Enable 3.5 only when an application explicitly requires it; otherwise, keep the newer .NET components that Windows and other applications already use.

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