If I double-click on the Notepad++ icon, it opens the last document used. Is there any way to have it default to a blank new document when opened? Is there an argument I can pass in via the shortcut or something?
Uncheck the Remember current session for next launch" checkbox in
Settings->Preferences->MISC`. (Image from Notepad++ v6.4.5 (Aug. 9, 2013), Unicode.)
As has been noted below. the checkbox has been moved to the Backup tab in more recent versions: