Password to open the document:
If it is applied then you have to give the correct password to open the workbook. Otherwise you cannot open the workbook.
Password to modify the document:
If it is applied then you have to give the correct password to modify the workbook. Otherwise your workbook is opened but you cannot modify the workbook. It means that your workbook becomes read-only.
To apply a password to MS Excel document, follow the given steps:
1. Open the file
2. Click on Tools menu and select “Options” from the menu.
3. Select the “Security” tab.
4. Enter “Password to Open”
5. Enter “Password to Modify”
6. Click On OK
7. Verify the passwords by re-entering both of them.
8. Save the document and close it
9. Re-open the document and check the passwords.