every time i open a document with preview, it insists on opening all the documents i had open before. i must be doing something wrong, and find a different workflow, maybe instead of closing the app, i need to manually close each document that i don't need anymore. i guess it's not an issue if you use preview often and keep it running all the time, but i rarely need it since most of what i do is either terminal or br…
There might be a way to turn it off but in the meantime you can press command-option-W to close all windows.
EDIT: You can disable this globally in System Preferences, or on a per-app basis by writing to the app's defaults:
defaults write com.apple.Preview NSQuitAlwaysKeepsWindows -bool false