Spreadsheet
Excel: 'file format or extension is not valid'
This message almost never means the data is gone. It means the ZIP container Excel expects (an .xlsx is a zip of XML parts) has a damaged header, a truncated tail, or the file was actually saved in a different format than its extension claims.
Stop doing this first
- Do not let Excel re-save over the original file.
- Do not run cleanup or 'optimise' tools on the drive holding it.
- Do not delete temporary ~$ files in the same folder — they can hold a usable copy.
The safe order of operations
- 1
Copy the file somewhere else and work only on the copy — everything below is done on the copy.
- 2
Check the real format: if the first bytes are PK it is a modern .xlsx zip; D0 CF 11 E0 means it is really an old .xls that was renamed.
- 3
Rename the copy to .zip and try to open it. If the archive lists xl/workbook.xml, your data is still in there.
- 4
Use Excel's own Open → Open and Repair on the copy, then 'Extract Data' if repair fails.
- 5
If the zip is truncated, repair the archive first, then reopen it as .xlsx.
Commands that do the work
Identify what the file really is
file broken.xlsx && head -c 8 broken.xlsx | xxdInspect the OOXML parts
cp broken.xlsx copy.zip && unzip -l copy.zipRepair a truncated archive
zip -FF copy.zip --out fixed.zip && cp fixed.zip fixed.xlsxConvert with LibreOffice (often reads what Excel refuses)
soffice --headless --convert-to xlsx --outdir out/ broken.xlsxRealistic odds
Usually likely recoverable — full recovery when the zip directory survives, partial when the tail is truncated.
Your case will differ in the details. Load this scenario into the recovery form and add what you already tried — you'll get a plan for your exact situation.
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