When inserting notes in Preview app, apostrophes become double-byte characters
That's the "smart quotes" feature converting the plain ASCII quote to a fancy (curved) Unicode quote (which is two bytes in UTF-8 encoding). You can turn this off with System Preferences -> Keyboard pane -> Text tab -> deselect "Use smart quotes and dashes". Note that this is a system-wide setting, so it'll affect most word processors as well as Preview.