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A Windows file type is commonly identified by its filename extension—the characters after the final period, such as .xlsx in expenses.xlsx. The extension helps indicate what kind of file it is and which apps may open it, but it is a clue rather than a guarantee. You can reveal extensions in File Explorer, check available apps, and set a default app in Windows settings.
What is a Windows file type?
A filename usually has a name and an extension separated by a period. In expenses.xlsx, expenses is the name and .xlsx is the extension. Windows uses extensions to help identify file types, associate them with apps, and choose an icon in File Explorer. An extension does not prove what the file contains, and more than one installed app may be able to open the same type.
Microsoft’s common file extension guide lists examples including:
| Extension | Typical file type |
|---|---|
.docx |
Word document |
.xlsx |
Excel workbook |
.pdf |
Portable Document Format file |
.jpg or .jpeg |
Photo |
.mp3 |
Audio file |
.mp4 |
Video file |
.zip |
Compressed file |
.exe |
Executable program |
These are familiar examples, not a complete list of formats or compatible apps.
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How to show file extensions in Windows
- Open File Explorer.
- Select View > Show > File name extensions.
With extensions visible, you can distinguish filenames such as report.docx and report.pdf. In earlier File Explorer layouts, Microsoft also documents View > Options > Change folder and search options as an alternative route to folder settings. Labels may differ by Windows release.
How to open a file with an unfamiliar extension
First check whether Windows offers an installed app that can open it. Right-click the file and select Open with > Choose another app to review available options. You can also choose Open with > Search the Microsoft Store, or search the extension in Microsoft Store. Windows may not identify an app for every extension, and a suggested app is not proof that the file is safe or that its contents are genuine.
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How to change the default app for a file type
If you want a particular app to open that type whenever you open a file, go to Settings > Apps > Default apps. Search for the extension or link type, select it, and choose an app. You can also select an app in Default apps to review which file types it can open. See Microsoft’s instructions for changing default apps. This guidance covers Windows 10 and Windows 11; interface labels can vary by release.
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No. Changing a filename from report.docx to report.pdf changes the name, not the data format. The renamed file may fail to open or behave incorrectly because its contents were not converted. To change formats, use an application or workflow that supports conversion for the file’s actual format; renaming alone is not conversion.
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Windows version context
Microsoft’s extension guidance applies to Windows 10 and Windows 11. Windows 10 support ended on October 14, 2025, so readers still using Windows 10 should account for that support status when considering ongoing security and updates.
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