In some instances, the files open well on different browsers and in file desktop apps like Excel but fail in other Microsoft apps.

Here is a tutorial to lock or hide only the formula cells in an Excel workbook. You can also lock formulas in all worksheets in a workbook.

Unlock Excel Workbook without Software TL;DR Key Takeaways : Verify the Excel file is protected by checking for restricted actions or password prompts when attempting to unprotect it.