If you have installed Windows 8, you might have seen that when you try to install some softwares, a window pops up saying "An app on your PC needs the following feature: .NET Framework 3.5" as shown on the picture below.
So, here is my trick to enable/install .NET framework 3.5 manually without downloading the file (No internet connection Required). Follow the step by step tutorial below:
Step 1: Insert the Windows 8 disc.
Step 2: Run Command Prompt (cmd) as Administrator.
Step 3: Now, just copy and paste the below code (the G on Red color is your Disc Drive letter, replace it with your disc drive letter) on command prompt and hit 'enter'.
dism.exe /online /enable-feature /featurename:NetFX3 /Source:G:\sources\sxs /LimitAccess