Download Net Framework 3.5 Windows 10 64 Bit Offline Installer !full! Info

How to Install .NET Framework 3.5 on Windows 10 Without an Internet Connection

Do not search for a separate offline redistributable.
Do obtain the Windows 10 installation ISO.
Use DISM with the /Source parameter pointing to the sxs folder from the ISO.

Corporate firewalls blocking Windows Update
Metered or slow internet connections
Corrupted Windows Update cache
Group Policy restrictions on managed PCs

She walked him through it:

Press Enter. The progress bar will reach 100%, and .NET 3.5 will be fully enabled. Method 2: Manual Download from Microsoft How to Install

The Problem: Online Installer vs. Offline Installer

Windows 10 offers an online installer. When you enable .NET 3.5 via "Windows Features," Windows Update downloads the required files. This sounds easy, but it fails frequently due to: Do not search for a separate offline redistributable

DISM logs: check C:\Windows\Logs\DISM\dism.log for details.