annotation font size
The default font size for annotations is too small. Either make it bigger (e.g. at least 11 points) or provide an option to change it.
The font size can be changed by clicking on the annotation to select it, pressing the “Style” button on the menu that appears then changing the font size option.
To add to my previous comment, you can change text size for free-text annotations, but not for comments in the side bar. If you're using a browser that has a developer mode (e.g., Firefox, Chrome) you can edit the CSS and change the .staticNoteContents class to have, e.g., font-size: 16pt;
This doesn't seem to be true, or not anymore. Now the style menu for note annotations only show color and opacity, not font size.