Unable to open some excel files

The error indicates that the file’s actual contents do not match the Excel format implied by its extension (for example, a non‑Excel file renamed to .xlsx) or that the workbook is corrupted.

Use these checks and recovery steps:

1. Confirm the file type

• Check whether the file was renamed manually (for example, from .txt or .csv to .xlsx).
• If the file was renamed inadvertently, open it in Excel and then save it with the correct file type/extension.
• If it was intentionally renamed just so Excel would recognize it, open it and then save it using a file name extension that reflects the real format.

2. Verify the source and safety

• Only proceed if the file comes from a trusted source. A malicious user could rename a non‑Excel file to .xlsx to trick Excel into opening it.

3. Try opening from local storage

• If the file is an email attachment, first save it to the Mac (Downloads or Documents), then open it directly from Excel instead of from the mail app.
• If that still fails, ask the sender to resend it as:
  • Excel Binary Workbook (*.xlsb), or
  • Excel 97‑2003 Workbook (*.xls).

4. Handle possible corruption

• If the workbook is corrupted and no longer resembles a valid Excel format, use Excel’s repair options as described in the “Repair a corrupted workbook” article referenced in the documentation.

If none of these steps work for specific files while others open normally, those particular files are likely either not genuine Excel workbooks or are too damaged for Excel to recover.

References:

• A file is in a different format than its extension indicates in Excel