Windows File Formats and Default Applications

By Martin Jansen, Owner of Jansen-PCINFO

Recently, one of my customers attempted to install Microsoft 365 on his new Dell Laptop.  The installation went well until he discovered that he would have to pay a subscription fee of $100 per year for the family plan ($70 for a personal plan).  The reason he installed it in the first place was that someone sent him a spreadsheet that he wanted to open and enter some data.

Coming from the business world, my customer thought that Microsoft Excel was the only answer for opening the file.  On the contrary, there are many free office suites that can open .xlsx files.  LibreOffice is one of my favorites, but WPS Office, Apache OpenOffice, FreeOffice and Google Sheets can open the files.  Microsoft has its own limited online versions of Word, Excel and Powerpoint, but you will be limited to 5 GB of storage compared to Google’s 15 GB storage and you will be prompted to purchase the full version of Microsoft 365 with 1 TB of space.

File Format Mess

Windows, like many operating systems, uses file extensions (like .docx for Microsoft Word) to manage which applications open when double clicking on a file.  My customer’s attempt to install Microsoft 365 really messed up the associations.  When he double clicked on the file sent to him, it opened Excel, but there was a warning at the top that Microsoft 365 was not activated and he could not enter any data in the cells.  And, of course, activating 365 would cost him $100.  Full circle.

Installing 365 also took over the .ods format which stands for OpenDocument Spreadsheet.  Excel can open these files, but will not write the files without losing some formatting.  When I opened the previously installed LibreOffice the app warned that the .ods extension was in use by another application – Excel.  In fact, Microsoft 365 would like to take a lot of extensions on a computer.  

Changing Extension Associations

So, we know that Microsoft is an extension hog:  We can change the extension associations by following these steps:

  1. Right (not left) click on the Start Button
  2. Select Settings
  3. Select Apps
  4. On the left side select Default apps
  5. Scroll down and select Set defaults by app

Then fix each file association for instance in this chart I associate the extension with the three most commonly used LibreOffice Applications:

Document Related File Formats
ExtensionFormat TypeAssociated Application
.docWord 97-2003 DocumentLibreOffice Writer
.docmWord Macro-Enabled DocumentLibreOffice Writer
.docxWord DocumentLibreOffice Writer
.docxStrict Open XML DocumentLibreOffice Writer
.dotWord 97-2003 TemplateLibreOffice Writer
.dotmWord Macro-Enabled TemplateLibreOffice Writer
.dotxWord TemplateLibreOffice Writer
.odtOpenDocument TextLibreOffice Writer default format
.pdfPDFAll modern wordprocessing applications can save or export PDF files.
.rtfRich Text FormatLibreOffice Writer
.txtPlain TextLibreOffice Writer
.wpsWorks 6-9 DocumentLibreOffice Writer
Spreadsheet Related File Formats
ExtensionFormat TypeAssociated Application
.csvCSV (Comma delimited)LibreOffice Calc
.odsOpenDocument SpreadsheetLibreOffice Calc default format
.pdfPDFModern spreadsheet software can save as PDF, but must watch formatting which can exceed margins or make the text tiny and unreadable
.prnFormatted Text (Space delimited)LibreOffice Calc
.txtText (Tab delimited)LibreOffice Calc
.xlsExcel 97-Excel 2003 WorkbookLibreOffice Calc
.xlsMicrosoft Excel 5.0/95 WorkbookLibreOffice Calc
.xlsbExcel Binary WorkbookLibreOffice Calc
.xlsmExcel Macro-Enabled WorkbookLibreOffice Calc
.xlsxExcel WorkbookLibreOffice Calc
.xltExcel 97 – Excel 2003 TemplateLibreOffice Calc
.xltmExcel Macro-Enabled TemplateLibreOffice Calc
.xltxExcel TemplateLibreOffice Calc
.xlwExcel 4.0 WorkbookLibreOffice Calc
Presentation Related File Formats
ExtensionFormat TypeAssociated Application
.odpOpenDocument PresentationLibreOffice Impress default format
.pdfPDFModern presentation software can save as a PDF
.potPowerPoint 97-2003 TemplateLibreOffice Impress
.potmPowerPoint Macro-Enabled TemplateLibreOffice Impress
.potxPowerPoint TemplateLibreOffice Impress
.ppaPowerPoint 97-2003 Add-InLibreOffice Impress
.ppamPowerPoint Add-InLibreOffice Impress
.ppsPowerPoint 97-2003 showLibreOffice Impress
.ppsmPowerPoint Macro-Enabled ShowLibreOffice Impress
.ppsxPowerPoint ShowLibreOffice Impress
.pptPowerPoint 97-2003 PresentationLibreOffice Impress
.pptmPowerPoint Macro-Enabled PresentationLibreOffice Impress
.pptxPowerPoint PresentationLibreOffice Impress

Another Way

Perhaps an easier way is to reinstall the application to fix file associations:

  1. Type WIN+R and enter appwiz.cpl
  2. Uninstall Office 365 and leave the extensions abandoned
  3. Uninstall LibreOffice
  4. Reinstall LibreOffice to recapture the associated extensions

Default Applications

On the way to changing extensions, the steps take you through the default apps.  Microsoft would very much like you to use Edge as your default browser.  Edge is based on Google Chrome, but many would just like to have Chrome as their default browser.

After you install Google Chrome, it does not become your default browser.  You must change the default app in settings.  When you change the default browser from Edge to Chrome a warning box appears reading, basically, that Edge is better – please don’t change.  Microsoft’s claim is not true, but, when did facts get in the way of big business?  Make the change anyway and enjoy Chrome just like you are used to doing.

Even then, you can’t uninstall Edge conventionally.  It pops up whenever you click on Microsoft sponsored content.  Here is a guide from Tom’s Hardware if you really want to uninstall the browser.  It’s simply not worth the hassle if you ask me.


In Windows use Default Apps to fix the extensions associated with the applications.  Search for Default Apps in both Windows 10 and 11.  Scroll to the button to select Set defaults by app and find the extension that is opening the wrong app.  On the way, if you want to install another browser, this is where you can change from Edge.