Need to Install .NET Framework 3.5 for NI Software on Offline Computer

When running an NI installer, I get a message similar to the one below:

Microsoft .NET Framework 3.5 is required before you can install this product. 

I try to continue but I do not have an internet connection. Why do I need an internet connection to install the .NET Framework 3.5? 

How do I install the .NET Framework 3.5 on an offline computer? 

Some versions of Microsoft Windows do not allow third party software to install .NET Framework 3.5 from media. If the .NET Framework 3.5 is not already present, download and install it before proceeding with installation of NI software. You have two options to install from an offline computer:
 

1.  Connect the computer to the internet and rerun the installer. Click OK and allow Microsoft to download the .NET Framework 3.5 and install it on your computer. For other online methods to install it, visit Microsoft's help page . 
2.  Use your Windows media or the Microsoft Windows Deployment Image Servicing and Management (DISM) tool to install .NET Framework 3.5 offline. For more information on how to use these offline methods, visit Microsoft’s website .