I have a clean install of Windows 8 on a partition, with Visual Studio 11/2012 Professional installed and I cannot find regtlibv12.exe inside C:\\Windows\
(Or you can use chocolatey https://chocolatey.org to install both of the above: package names are 7zip and lessmsi respectively.)
dotNetFx40_Full_x86_x64.exe from the previous step, extract the files netfx_Core_x64.msi and netFxCore.mzz to a temporary directorynetfx_Core_x64.msi, scroll down the file list and select regtlibv12.exe (the one with Component = regtlibv12_exe_amd64 for an x64 system, the other one for x86, or both if you need both) and click the "Extract" buttonregtlibv12.exe!regtlibv12.exe (regardless of the fact that doing so would be illegal, if you think you need to - you either don't, or your software has big problems).