Open the Excel file
Click File
Click Info
Click Protect Workbook
Select Encrypt with Password
Enter a password
Re-enter the password
Click OK
Save the file
To lock a worksheet
Open the sheet
Click Review
Click Protect Sheet
Enter a password
Choose allowed actions
Click OK
Re-enter the password
Click OK
To lock specific cells
Select the cells
Right-click and choose Format Cells
Click the Protection tab
Check Locked
Click OK
Click Review
Click Protect Sheet
Enter a password
Click OK
To lock the workbook structure
Click Review
Click Protect Workbook
Check Structure
Enter a password
Click OK
To remove protection
Click Review
Click Unprotect Sheet or Unprotect Workbook
Enter the password
Click OK