"The file format or extension is not valid".
Excel showed "The file format or file extension is not valid" before it could open your workbook. That can mean the file is not really an .xlsx, or that damage prevents Excel from recognizing the package. Upload the file and the watermarked preview will show whether a validated workbook could be rebuilt. A one-time $14 USD — and only if the repair works.
Free preview — pay only if you download ($14 USD)
Your files auto-delete — delete them sooner anytime
No person looks at your file as part of repair
Uploading your file.
Keep this tab open while the file transfers. Large files can take longer.
Starting upload...
Recovering what we can.
- Upload received
- Repair in progress
- Result ready
Analyzing your file...
Here's what we recovered.
Review the watermarked preview before checkout.
Repair your file
Choose a supported file to see what can be repaired before checkout.
Simulated checkout — no payment is processed.
Optional — we'll email your private download link.
You preview before you pay. If the download is materially worse than the preview you approved, we'll refund you.
Your files auto-delete — delete them sooner anytime
No person looks at your file as part of repair
We couldn't recover this one.
The file is too damaged to rebuild, so there is nothing to preview and no charge.
What stopped you continuing? One tap tells us why.
Try a deep repair
The repair engine can try a longer pass on the file you already uploaded.
Machine-only processing; no human views files; nothing is sent to an outside AI.
Have another clip from the same device?
A healthy video recorded on the same device — ideally the same settings — gives the repair engine a template to rebuild from. It can unlock repairs that fail on their own.
Unrepaired files are kept encrypted for up to 30 days, then deleted.
FileFix can't fix that kind of file yet.
Right now we repair video, audio, document, and image files (MP4, MOV, M4V, MKV, AVI, TS, MTS, M2TS, MPG, MPEG, VOB, 3GP, WebM, FLV, M4A, WAV, MP3, AAC, FLAC, OGG, OPUS, AIFF, XLSX, DOCX, PPTX, ODT, ZIP, RAR, PDF, AI, HEIC, and HEIF). We're adding support for more formats over time.
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Why this happens
"The file format or file extension is not valid" is an identity check, not a diagnosis. Excel shows it when the filename extension and the bytes do not describe a workbook it can parse. A renamed .xls, CSV, HTML file, or unrelated download can trigger it, and so can a damaged .xlsx ZIP header or missing package records.
Changing the filename to .xlsx does not convert another format and does not restore missing ZIP records. FileFix looks at the uploaded bytes, scans recoverable members, and only returns an .xlsx when it can rebuild and validate actual workbook content.
If the file is genuinely an older .xls workbook or another document type, this .xlsx repair is not the right converter. If it is a damaged .xlsx, the free watermarked worksheet preview provides evidence from the rebuilt output before checkout.
What we can and can't recover
We can usually fix
- Files that show "Excel found unreadable content"
- Files Excel calls an invalid format or extension
- Workbooks cut off mid-save or mid-transfer
- Files that show the right size but won't open
We can't fix
- Password-protected/encrypted workbooks
- Genuinely empty (0-byte) files
- Deleted or formatted files (that's data recovery, a different job)
- The old binary .xls format (this repair is for .xlsx)
How it works
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Upload Drop the file in. It uploads over an encrypted connection. The repair runs automatically — no person looks at your file.
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Free watermarked preview You see watermarked pages of the recovered worksheets.
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Pay & download If the preview shows what you need, unlock the repaired Excel file for a one-time $14 USD.
You see watermarked pages from your rebuilt workbook before you decide anything — so you never guess.
See what's recoverable.
Free watermarked page preview · private & auto-deleted
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Questions
No. Renaming changes only the label, not the file structure. Use Excel or another spreadsheet app to convert a healthy .xls; FileFix does not convert the old binary format.
The repair scans for ZIP members used by modern Office files. It routes a package with Excel worksheet members through the .xlsx rebuild and then requires the result to open as a workbook.
An HTML error page does not contain workbook members, so the engine cannot turn it into the missing spreadsheet. Download the source file again from the original service.