File Format & Compatibility

How to Fix Excel Files Opening as PDFs After Installing Microsoft 365

Maira Mehtab Sep 21, 2026 868 views

Question details

Users are experiencing an issue where existing XLS and XLSX spreadsheet files appear as PDF documents or open in a PDF reader instead of Microsoft Excel following a Microsoft 365 installation.

Product: Microsoft Excel
Device & OS: Windows
Scenario: Attempting to open existing Excel spreadsheet files (.xls, .xlsx) from the computer after successfully installing Microsoft 365.
Observed behavior: The Excel files incorrectly launch in a default PDF reader rather than Microsoft Excel, usually accompanied by the file icons changing to PDF icons.

Before you start

Ensure that Microsoft 365 is completely installed on your computer and locate at least one affected XLS or XLSX file in your File Explorer to use for testing.

Solution 1Recommended

Use the Open With Context Menu to Reassign the App

This is the quickest method to reassign the default application for a specific file type directly from the file itself.

Right-click the affected file

Locate an existing XLS or XLSX file on your computer and right-click on it to open the context menu.

Select Open with

Hover over or click 'Open with' from the dropdown menu to see a list of available applications.

Choose Microsoft Excel

Select 'Microsoft Excel' from the list of programs. If it is not immediately visible, click 'Choose another app' to find it.

Set as the permanent default

Check the box that says 'Always use this app to open these files' (or similar wording depending on your Windows version), then click OK.

Icon Restoration: Once you complete this process, the file icons should automatically revert from the PDF icon back to the standard Excel spreadsheet icon.

Solution 2

Configure Windows Default Apps Settings

Use this method to change the file associations for multiple spreadsheet extensions at once through the Windows system settings.

Free Microsoft Office alternative

Try WPS Office for Seamless Spreadsheet Management

If you frequently run into software conflicts, file association issues, or heavy installation problems with Microsoft 365, WPS Office provides a free, lightweight, and easy-to-use alternative. It sets up in seconds and manages all your document types without hassle.

1. Download and Install: Download the free WPS Office installer from the official website and follow the quick setup wizard.
2. Open Your Spreadsheets: Launch WPS Spreadsheet and instantly open your existing XLS and XLSX files with perfect formatting.
3. Set as Default: Easily set WPS Office as your default program to automatically handle all future spreadsheet files without conflicts.

Free to use with a lightweight, fast installation processFully compatible with Microsoft Excel formats (.xls, .xlsx, .csv)Familiar tabbed user interface ensuring a zero-learning-curve transitionBuilt-in PDF editing and spreadsheet tools combined in one app

microsoft office alternative - wps office

Frequently Asked Questions

Why did my Excel files turn into PDFs after installing Microsoft 365?

This occurs when Windows incorrectly overrides or alters default file associations during the software installation. It assigns your spreadsheet file extensions (.xls, .xlsx) to your default PDF reader instead of properly mapping them to the newly installed Microsoft Excel.

Will changing the default app affect or damage the data inside my Excel files?

No, changing the default app only tells the Windows operating system which program to use to open the file. Your underlying spreadsheet data, formulas, and formatting remain completely unchanged and safe.

How do I fix the file icons if they still look like PDFs after changing the settings?

If the file icons do not immediately update after you reassign the default app to Microsoft Excel, restarting your computer or restarting Windows Explorer will usually refresh the system icon cache and restore the standard Excel icons.

Can I set default apps for older Excel formats like .xls specifically?

Yes. By using the 'Choose default apps by file type' menu in Windows Settings, you can manually locate the older .xls extension and assign Microsoft Excel as the primary application independently of the newer .xlsx format.

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