How to unprotect Excel sheet if forgot the password

If you have lots of sheets to unprotect, Notepad++ allows regular expression based search and replace, which is really useful. Open all your sheets at once with Notepad++, select Search and Replace, select the Regular Expression radio button for your search type and then use <sheetProtection.+?/> as your search term. This will find the section that you need to delete across all your sheets. Replace with blank and then hit "Replace all in all opened documents". You've got 'save all' and 'close all' buttons to commit your changes too. Final tip - don't click "Enable Content" when you open the spreadsheet in case the person who protected the sheet put in a sneaky macro to re-enable protection.