If I created an excel sheet, clicked protect sheet with password added, how come when others sent the excel sheet back to me, the "protect sheet" option is no longer there? It's as the sheet was never protected in the first place.
Is there anything I can do to prevent others from unlocking my sheet without password?
I think so, if the person has enough skills (s)he could remove the protection. Yu may try yourself, the easiest way - upload protected file to Google Sheets and download it back as Excel file. Most probably protection will be lost. You may corrupt the file by such way, depends on formulae used, but there are other ways.
