If you see errors stating "cannot open include file: 'windows.h'", it usually means the include paths are broken. Re-running the Visual Studio Installer and performing a "Repair" on the 2017 installation usually fixes this registry mapping issue. Retargeting Solutions

Once installed, you must tell your Visual Studio 2017 project to utilize the older SDK instead of the Windows 10 version. Open your solution in Visual Studio 2017.

The most reliable way to get the Windows 8.1 SDK for Visual Studio 2017 is through the Visual Studio Installer rather than a standalone download. This ensures the IDE correctly maps the paths to the SDK. Step 1: Open Visual Studio Installer Launch the "Visual Studio Installer" from your Start menu. Step 2: Modify Your Installation

Scroll down to the "SDKs, libraries, and frameworks" section. Look for: Windows 8.1 SDK Check the box next to it. Step 5: Finalize Installation

If you need to install the SDK on a machine without internet access or for CI/CD pipeline configurations, you can download the standalone installer directly from the Microsoft hardware dev center. Visit the official Microsoft Windows SDK archive. Search for "Windows SDK for Windows 8.1." Download the sdksetup.exe file.