The .NET Framework 3.5 is a critical runtime requirement for legacy applications and games built between 2005 and 2011. While Windows 10 comes with .NET Framework 4.x pre-installed, it does natively support apps designed for versions 1.1 through 3.5.
: Type the following command, replacing D: with your actual drive letter:
: The process will reach 100% and show "The operation completed successfully".
If you are working in an environment without internet access or frequently encounter errors like or 0x800f081f when using the standard Windows Update method, you will need an offline installation strategy. Official Offline Installer Options
DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:D:\sources\sxs