This shortcut is normally used to open Format menu but that depends
Alt + O
- Opens up the menu with the letter O underlined in all programs that have such a menu. Normally and especially for text editors that letter is reserved for the Format menu
- WinRAR – Opens up the Favorites menu
- GOM Player – Opens subtitles
- KMPlayer – Loads the subtitle
- Microsoft Outlook – Displays the Format menu
- In some programs it opens the Options menu
- Google Chrome: also opens the format menu
- ACDSee: Opens the Options menu
If you’re unsure about it just go ahead and try it ;)