Repair Corrupted Excel Workbook

My main Excel workbook refuses to load correctly. The moment I try to open it, Excel throws the warning:
“Excel cannot open the file because the file format or file extension is not valid.”
If I continue, the file does open, yet every sheet is visibly corrupted—numbers, formulas and formatting are all unreadable.

The goal is simple: restore this file so it opens in modern Microsoft 365 without errors and displays its original data, formulas, charts and pivots intact.

You may rely on any recovery approach—built-in repair, VBA, third-party tools, hex or binary editing, even temporary conversion through LibreOffice—as long as the outcome meets the criteria below.

Acceptance criteria
• A clean .xlsx that opens with zero error prompts
• Original sheet structure, formulas and data preserved as fully as possible
• A short report noting anything that could not be salvaged

Send your estimated turnaround time and any clarifying questions, and we can get started right away.