This method is for users who want to have the option of quickly opening unknown file types in Notepad.
Navigate to Start, type regedit in the search box and press enter.
Scroll down to the following key:
Right click on shell and select New – Key from the drop down list.
Name the new key Open with Notepad.
Create another new key called Command in the right hand pane.
Double click on the (default) value in the right hand pane and enter in the following:
Exit out of Registry Editor and be sure to check if any file has the additional option Open with Notepad in its Context menu (as shown below).