Offline install of .NET Framework 3.5 in Windows 10 using DISM

Windows 10 comes with .NET framework 4.5 pre-installed, but many apps developed in Vista and Windows 7 era require the .NET framework v3.5 installed along with 4.5. These apps will not run unless you will install the required version. When you try to run any such app, Windows 10 will prompt you to download and install .NET framework 3.5 from the Internet. However, this will take a lot of time. You can save your time and install .NET Framework 3.5 from the Windows 10 installation media. This method is much faster and does not even require an Internet connection. Here is how to install it.

To install .NET Framework 3.5 in Windows 10, do the following:

1. Insert your Windows 10 DVD, or double click its ISO image, or insert your bootable flash drive with Windows 10, depending on what you have.
2. Open 'This PC' in File Explorer and note the drive letter of the installation media you have inserted. In my case it is disk D:
   
3. Now open an elevated command prompt and type the following command:

   Dism /online /enable-feature /featurename:NetFX3 /All /Source:D:\sources\sxs /LimitAccess

   Replace D: with your drive letter for Windows 10 installation media.
   

You are done! This will install .NET framework 3.5 in Windows 10.

To save your time, I have prepared a simple batch file which will save your time and will find the inserted installation media automatically. It looks like this:

@echo off
Title .NET Framework 3.5 Offline Installer
for %%I in (D E F G H I J K L M N O P Q R S T U V W X Y Z) do if exist "%%I:\\sources\install.wim" set setupdrv=%%I
if defined setupdrv (
echo Found drive %setupdrv%
echo Installing .NET Framework 3.5...
Dism /online /enable-feature /featurename:NetFX3 /All /Source:%setupdrv%:\sources\sxs /LimitAccess
echo.
echo .NET Framework 3.5 should be installed
echo.
) else (
echo No installation media found!
echo Insert DVD or USB flash drive and run this file once again. 
echo.
)
pause

Download the file, extract it from the ZIP archive to the Desktop, right click it and choose Run as administrator. The file will install .NET Framework 3.5 automatically after finding the drive letter of your Windows 10 installation media.

Source : https://winaero.com/offline-install-of-net-framework-3-5-in-windows-10-using-dism/