SharePoint Designer file
File type: Various data file
The .spdesignunknown file extension identifies a SharePoint Designer file associated with Microsoft Office SharePoint Designer.
Office SharePoint Designer is a Windows application for creating and modifying Microsoft SharePoint sites and web pages.
File type category:
Various data file
Date updated: September 27, 2026
Microsoft Office SharePoint Designer is a specialized HTML editor and web design program for creating and modifying Microsoft SharePoint sites and web pages. A .spdesignunknown file is associated with that application.
The extension identifies a SharePoint Designer-related file, but it does not describe a standard standalone document format or reliably indicate the file's contents. It should be handled within the SharePoint Designer workflow rather than renamed to another extension.
Office SharePoint Designer is legacy Microsoft Windows software and is no longer developed as a current web-authoring tool. Existing files may still require the Windows application that created or used them.
Open a .spdesignunknown file on Windows with Microsoft Office SharePoint Designer. Start the application and use its Open command, or open the file from Windows if the file association is configured.
If the file does not open by itself, access it through the SharePoint site or project with which it was created. The extension does not guarantee that it is an independently readable document.
There is no established general-purpose converter for .spdesignunknown files. Renaming the file extension does not convert the file.
If the file is part of SharePoint site content, open the relevant site or project in Office SharePoint Designer and use the application's available publishing or export functions to save the content in another form.
Software applications that handle other tasks involving spdesignunknown files:
Microsoft Windows
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