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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsA Windows file type is commonly identified by its filename extension: the letters after the final period in a name, 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. Windows files can often be opened by more than one app.
What is a file extension in Windows?
A filename usually has a base name and an extension separated by a period. In expenses.xlsx, expenses is the base name and .xlsx is the extension. Windows uses extensions to help identify file types, suggest compatible apps, and choose the icon shown in File Explorer. Microsoft Support explains common Windows file extensions.
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An extension does not prove what is inside a file, nor does it identify a single app that must open it. Several installed programs may support the same extension, and a misleading or changed extension may not match the file’s actual contents.
Common Windows file extensions
| Extension | Common file type |
|---|---|
.docx |
Word document |
.xlsx |
Excel workbook |
.pdf |
Portable Document Format file |
.jpg, .jpeg |
Image or photo |
.mp3 |
Audio file |
.mp4 |
Video file |
.zip |
Compressed archive |
.exe |
Executable program |
These are examples, not a complete list of Windows formats or compatible applications. The app available to open a file depends on what is installed and supports that type.
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How to show file extensions in File Explorer
- Open File Explorer.
- Select View > Show > File name extensions.
On some interface layouts, the setting is under View > Options > Change folder and search options. Showing extensions makes it easier to distinguish similarly named files and to inspect an unfamiliar suffix. Microsoft’s File Explorer guidance documents these options.
How to open a file with an unfamiliar extension
- In File Explorer, right-click the file and select Open with > Choose another app to review installed options.
- If no suitable installed app appears, search for the extension in Microsoft Store. You may also see Open with > Search the Microsoft Store.
- Choose an app only if it supports the file type; Store or Windows suggestions do not guarantee that every extension has an available compatible app.
These are ways to discover possible apps, not a guarantee that a file is safe or that it will open successfully. Microsoft Support describes both the installed-app and Store-search options.
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How to change the app that opens a file type by default
If you want one app to open that type whenever you open a matching file, use Windows default-app settings. The path documented by Microsoft is Settings > Apps > Default apps.
- Open Settings > Apps > Default apps.
- Search for the extension or link type, select it, and choose the app you want.
- Alternatively, select an app in Default apps to review the file types it can open.
Labels and layout can vary by Windows release. Microsoft’s default-app instructions cover selecting by file type, link type, or application.
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Does renaming an extension convert a file?
No. Changing a filename suffix changes the name, not the file’s data or format. For example, renaming a file so its name ends in .pdf does not turn its contents into a PDF. Use an appropriate format-specific app or conversion workflow when you need a different format; simply renaming the extension is not conversion. Microsoft’s file-extension guidance makes this distinction.
Windows version context
Microsoft’s common-extension guidance applies to Windows 10 and Windows 11. Microsoft states that Windows 10 support ended on October 14, 2025; interface labels may also vary across Windows releases. See Microsoft’s guidance.
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