First you’ll need to copy Windows 8 setup files to your hard disk, or a Disk.
2. Now open Command Prompt as Administrator as mentioned here and then provide following command:
Dism /online /enable-feature /featurename:NetFx3 /All /Source:F:\sources\sxs /LimitAccess
Here “F:” represents the CD/DVD drive letter in your system which contains Windows 8 setup disc. Replace it with the correct drive letter according to your system.
If you extracted Windows 8 setup files in a directory, replace F:\sources\sxs with the correct path.
3. As soon as you execute the above mentioned command, Windows will start installing .NET Framework 3.5 in your system and it’ll not require Internet connection.
4. That’s it. Now you have installed .NET Framework 3.5 in Windows 8 without using Internet connection.
Now you will be able to install Microsoft Exchange Admin Tolls without any problem.