You have to use
defaults write in a slightly differently way with Preview and other sandboxed apps.
defaults write com.apple.Preview ... modifies (or creates) a plist file in ~ / Library / Preferences.
As pointed out, that's not where preview looks (or looks for) its preference file, which is in a nested subfolder of ~ / Library / Containers instead.
To modify the correct plist, use:
defaults write -app Preview ...
You'll need to make sure you have the correct key, too. I have the following keys in my preview preview:
"PVAnnotationFontSize_12" = 10; "PVAnnotationFontSize_17" = 10; "PVAnnotationFontSize_5" = "11.99199"; "PVAnnotationFontSize_6" = 10;
However, modifying ones does not change the text size for either Annotations or Notes. Annotations used to keep the last settings used. Notes do not seem to be editable in the UI.
Also, note that you do not need to use it to read a specific plist key. E.g.
defaults read com.apple.Preview PVAnnotationFontSize_5 EDIT: Having probed into the plist data and the text strings within the Preview app itself, I'm not convinced that there is an editable key for the font size or style in Preview's Notes.