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