Steps
1.Open start menu, write “regedit” in search box and hit “Enter”.
2.Click on “File” and select “Export” from menu to backup your registry.
Now you can roll back changes that you made mistakenly.
3.Explore the key “HKEY_CURRENT_USER \Software \Microsoft \Windows \CurrentVersion \ Explorer \FileExts\”. List of all file extensions will be displayed.
4.Search for file extension that you want to edit. Let’s take an example of pdf program. Explore .pdf file to remove it. Once you find it, click on right triangle and select “OpenWithList”.
5.You will see list of programs on right window panel. Right click on program that you want to delete and select “Delete” from menu. Click “OK” to make confirmation. Done! To delete another program, repeat above steps and so on.
6.Now Right click on program and select “Open With” from menu. You will see that pdf file option has been removed from menu.