File-level security refers to the capability to password-protect your Excel file, preventing users from opening or editing it.
Workbook-level: By entering a password, you can lock your workbook’s structure.

To apply a password to an Excel workbook follow these steps:

1. Open the Excel file you wish to secure.
2. Choose Protect Workbook from the Review tab.
3. Select Structure in the Protect Structure and Windows dialog box.
4. Enter a password to secure the workbook. …
5. Click OK. …
6. Close the file.