Hi All, i just received my PB603 (aka Leggo IBS) and here is my two cents after a little bit of usage. I found no track about it in the user guide so here it is.
When you take a note on a book or html article or anything else, a pop up menu will ask you to save the note as an image. This image can be modified on the device with a preinstalled dedicated software. You can do this by going into the book TOC or directly from the "Notes" area of the device.
For each note you will see a blocknote icon with a '+' sign on its left. Use the pen to tap on this icon (tapping on the note title will bring you to the page of the note) and it will open a spolier and let you see the image of the note. Now LONG PRESS on the image and from the pop-up menu choose 'Modify'. This will load the image inside a drawing software from where you can underline, handwrite some notes etc.
Hoping this helps someone and sorry for my bad english