This is the most reliable method for Windows 10 and 11, as it uses the source files already present on your Windows ISO or DVD. How to manage .NET Framework on Windows 10 and 11 - PDQ
Critics argue that installing an older framework introduces security vulnerabilities. However, Microsoft maintains .NET Framework 3.5 as a of Windows 10 and 11. It receives cumulative security updates through Windows Update once installed . Therefore, installing it offline does not create a permanent security risk, provided the system eventually connects to the internet for monthly patches. The risk lies in the legacy applications themselves, not the framework.
Before installing .NET Framework 3.5, ensure your system meets the following requirements: microsoft net framework 3.5 offline
You can use the built-in DISM (Deployment Image Servicing and Management) tool to install the feature directly from a Windows USB drive or ISO file.
In these cases, the —specifically the standalone executable dotnetfx35.exe or the use of the Deployment Image Servicing and Management (DISM) tool with a source media—becomes the only viable solution. This is the most reliable method for Windows
Here's a helpful piece of information:
DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:"X:\sources\sxs" Before installing
A true offline installer can be created by downloading the two cab files ( microsoft-windows-netfx3-ondemand-package.cab and its language equivalent) from the Microsoft Update Catalog and placing them in a local folder. Then, using DISM: