If you have a Graphics Viewer licence on your PC you can add comments to a chart but the comments cannot be stored back to the original data set. This is because comments are actually stored in the ".HED" file not the ".PLT". You are only viewing the ".PLT" file and do not have access to the ".HED" file so cannot write to it to store the comment. If you are just viewing the charts on the web page without the Graphics Viewer then you have no access to the data and are just viewing a representation of the data in chart format with no ability to interrogate data points etc.

The Web Server is designed as a method of distributing the quality information throughout an organisation (and beyond if you want) not as an interactive tool.