MobiOffice lets you protect your Spreadsheet on a file level, allowing no one to view the file unless they have the password.
Password-protect a Spreadsheet
1. Open your Spreadsheet. Tap the menu in the top right.
2. Tap Protect.
3. Type and retype the password.
4. Tap OK.
5. Save or Save as the Spreadsheet.
Remove the password
1. Open your Spreadsheet. Tap the menu in the top right.
2. Tap Unprotect.
3. Type your password.
4. Tap OK.