When sharing your work with others, people often protect the workbook for the security reason. Please follow the steps below to protect a workbook:
Step 1: Click the "File" Tab from the Ribbon;
Step 2: Click Info from the left navigation sidebar;
Step 3: Click Protect Workbook, then select "Encrypt with Password";
Step 4: In the Encrypt Document window, type in the password, then click OK;
Step 5: In the Confirm Password window, type in the password again to confirm, then click OK;
Step 6: The Protect Workbook button will be highlighted;
Step 7: Next time, when you open the file, you will need to enter the password.