msvcr120d.dll
This file is not a system component: not redistributable — the program was built wrong. Restore it from the source that installed it rather than downloading a replacement.
Do not download this DLL on its own
Searching for a missing DLL by name leads to sites that hand you that single file. It is one of the oldest and most effective malware delivery methods there is, and a system DLL from an unknown source is indistinguishable from a deliberately modified one. There is never a legitimate reason to obtain a runtime component that way.
What it is
The DEBUG version of the Visual C++ 2013 C runtime. The trailing "d" is the whole story: debug runtimes are installed with Visual Studio for developers and Microsoft explicitly does not allow them to be redistributed.
Where you see it: Small tools, university projects, game mods and beta builds compiled in Debug configuration by mistake.
You cannot fix this properly from your side and you should not try. The Visual C++ 2013 redistributable does not contain it, because no redistributable ever contains a debug runtime. The program needs to be rebuilt in Release configuration by whoever made it. Any site offering msvcr120d.dll is distributing a file Microsoft does not license for distribution, which tells you plenty about what else they will hand you. The same applies to msvcp120d.dll, msvcr100d.dll and every other name ending in "d.dll".
Why there is nothing to download here
There is no verified download we can offer for this one, because installing a file is not the fix. The steps above are what actually resolves it. That distinction matters: the sites ranking for this file name are selling a download that would not have helped even if it were safe.