There are multiple ways of annotating IDA databases: renaming, commenting, or adding bookmarks. However, sometimes there is a need for general notes for the database as a whole, not tied to specific locations.
Notepad window
The database notepad is a text input box which can store arbitrary text within the database, so you can add your notes and thoughts there instead of using separate software.
It can be opened using the menu View > Open subview > Notepad. 
There is no built-in shortcut for quick access, but you can add one, or open the Quick view (Ctrl–1), type “no” to select the entry and Enter to activate it.
