What is the installed program "Windows SDK" on my Windows 7 computer? Why it is not visible in Control Panel?

"Windows SDK" is an installed program on Windows 7 system managed by Windows Installer.

You will not see "Windows SDK" listed on "uninstall or change a program" in Control Panel, because it is flagged as a hidden system component in the registry (SystemComponent=1).

Information related to "Windows SDK" installed program:

Name: Windows SDK
Publisher: Microsoft Corporation
Size: 3256 KB
Version: 10.1.15063.137
System Component: Yes
Identifying Number: {FA9A34AF-4DE5-017D-DC1D-5BCDFC0BA2A3}
Install Location: 
Install Source: C:\ProgramData\Package Cache\{FA9A34AF-4DE5-017D-DC1D-5BCDFC0BA2A3}v10.1.15063.137\Installers\
Install Date: 20170729
Local Package: C:\windows\Installer\1f6290a.msi
Package Name: Windows SDK-x86_en-us.msi
Uninstall Command: MsiExec.exe /I{FA9A34AF-4DE5-017D-DC1D-5BCDFC0BA2A3}
Windows Installer: Yes

It is recommended to keep "Windows SDK" as an installed program.

⇒ "Windows SDK Desktop Headers x64" Installed Program on Windows 7

⇐ "Windows Runtime Intellisense Content - en-us" Installed Program on Windows 7

⇑ Hidden Installed Programs using Windows Installer on Windows 7

⇑⇑ Windows 7 Installed Programs