First, confirm whether the file extension matches the actual format. If it does not match, correct the extension or import it in the correct way; 1. Check and display the file extension to ensure that it is in valid formats such as .xlsx or .xls; 2. Open the file with Notepad to view the content and determine whether it is CSV, HTML or garbled code; 3. If it is CSV or text format, open it through Excel's "Data" → "Import from Text/CSV" function; 4. Try to use Excel's "Open and Fix" function to restore abnormal files; 5. Re-download or export files from the source system to avoid incomplete transmission; 6. Test opening on other devices to eliminate local environment problems; as long as you clarify the real format of the file and take corresponding actions, you can solve the problem that Excel cannot open.

The error you encounter: "Excel cannot open the file because the file format or file extension is not valid" is a common problem when using Excel. It is usually not because the file is really corrupt, but because of mismatched extensions, incorrect save methods, or abnormal file source .

Here are some common reasons and corresponding solutions:

? 1. The file extension does not match the actual format

The most common reason is that the file looks like .xlsx , but it is not actually a format supported by Excel .

for example:

• Save as .xlsx with text editor, but the content is CSV or plain text
• The downloaded file is incorrectly named .xlsx , which is actually .csv , .txt , or .zip

Solution:

• View the real file format:
  1. Open File Explorer → Click "View" → Check "File Extension"
  2. See if the file is really called xxx.xlsx or xxx.xls
• Try to modify the extension:
  • If the file is actually CSV, change it to .csv and open it in Excel (via "Data" → "Import from Text/CSV")
  • If you are not sure about the format, you can open it with Notepad to see the content structure

? 2. The file is a "pseudo Excel" file exported from a web page or system

Many systems export "Excel files" are actually HTML tables or text with style tags . Although they can be opened in Excel, if they are forcibly saved as .xlsx , they will not be opened next time.

Typical manifestations:

• Open it with Notepad to see HTML tags such as <table> , <code><tr> , <code><td> , etc.<li> The file size is small (several KB), but there is a lot of content</li> <p> <strong>Solution:</strong></p> <ul> <li> Open the file with Notepad and confirm whether there is an HTML tag</li> <li> Correct way: Don't change the extension directly, but:<ol> <li> Open the original file with Excel (even if an error is reported, select "Yes" to try to open it)</li> <li> Or use the Data tab → Import from Text/CSV</li> <li> After successfully opening, save as real <code>.xlsx format

? 3. The file is corrupted or the download is incomplete

If the file is interrupted during transfer, download or save, the data may be incomplete.

How to judge:

• The file size is exceptionally small (for example, only a few KB)
• Others can open it, but you can't
• It was able to open before, but suddenly it couldn't be opened

Solution:

• Re-download or copy the file
• Try opening it on another computer to confirm whether it is a problem with the file itself
• Use Excel's "Open and Fix" feature:
  1. Open Excel → File → Open
  2. Select File → Click the drop-down arrow → Select " Open and Repair "

? 4. Incompatible saving method was used (such as saving as "Web page" but renamed to .xlsx)

Someone manually changed the "Save as Web Page ( .htm; .html)" file of web page or Excel .xlsx , which will cause it to fail to open.

Solution:

• Do not change file extension manually
• Save Excel files correctly: Use "Save As" → Select "Excel Workbook (*.xlsx)"

? 5. Excel version or compatibility issues

Older Excel (such as 2003) does not support .xlsx and requires compatibility packages; while newer Excel may also report errors when opening certain encryption or special formats.

suggestion:

• Make sure your Excel supports this file format
• Update Office to the latest version
• If it is a special format such as .xlsb , .xlsm , etc., make sure you select "All File Types" to open it

Quick self-test checklist (try in order):

• [ ] Display the file extension and confirm whether it is a legal format such as .xlsx , .xls , etc.
• [ ] Use notepad to open the file to see if the content is HTML, CSV or garbled code
• [ ] If it is CSV/text, use Excel's "Import" function to turn on
• [ ] Try the "Open and Fix" function
• [ ] Re-download or re-export from the source system
• [ ] Test whether it can be turned on on other computers

Basically these common situations. Most of the problems lie in the point of " You think it's an Excel file, but it's not ." As long as you understand the real format of the file, the problem will be solved.

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