Open the Excel file
Click File
Click Info
Click Protect Workbook
Select Encrypt with Password
Enter a password
Click OK
Re-enter the password
Click OK
Save the workbook
Close and reopen the file to confirm the password protection
Open the Excel file
Click File
Click Info
Click Protect Workbook
Select Encrypt with Password
Enter a password
Click OK
Re-enter the password
Click OK
Save the workbook
Close and reopen the file to confirm the password protection