Notes about the WEBPART file extension:
Incorrect file associations could be the result of underlying issues within your PC system. As such it is highly recommended to scan your PC for invalid registry entries, unused processes and other unfavourable system settings to identify slowdown issues.
The WEBPART file type is primarily associated with 'SharePoint' by Microsoft Corporation. Office SharePoint Designer provides tools to automate business processes, build efficient applications on top of the Microsoft SharePoint platform, and tailor SharePoint sites. Beginning with Windows SharePoint Services 3.0, the SharePoint Web Part infrastructure is built on top of the Microsoft ASP.NET 2.0 Web Part infrastructure and Web Parts that derive from the ASP.NET WebPart class are completely supported in SharePoint. You create Web Parts in Microsoft Visual C# or Microsoft Visual Basic by using the Web Part Library template in Microsoft Visual Studio 2005.