: It manages the lifecycle of VSTO add-ins, ensuring they load correctly when you open an Office app.
VSTO versions historically aligned with Visual Studio and .NET versions: vsto 4.0 download
| Problem | Solution | |---------|----------| | “This add-in is not available” | Install VSTO 4.0 runtime and ensure .NET 4.x is enabled in Windows Features | | Installation fails with error 0x80070643 | Uninstall any previous broken VSTO version using Microsoft Fix It or cleanup tool | | Office 365/2016+ add-ins not loading | Verify VSTO 4.0 SP1 is installed and Office is up to date | | Multiple VSTO versions shown | Normal – versions 2.0, 3.0, 4.0 can coexist for backward compatibility | : It manages the lifecycle of VSTO add-ins,
The installation process for VSTO 4.0 is straightforward: you likely don’t need to reinstall.
If present (especially version 10.0.xxxxx), you likely don’t need to reinstall.