[luite]

I have tested a few viewers and found out that both WinDjView 1.0.3 and DjView 4.6 support line annotations. The UDS plugin does not show them (yet?).

If you want to experiment with annotations, try this:
djvused myfile.djvu -e 'output-all' > annotations.dsed

open annotations.dsed, if you have a hidden text layer, you will see things like: select 'pagename.djvu' ... set-txt ... . Choose your favourite page and add the following lines below the line "select 'pagename.djvu'":
set-ant
(maparea "" "" (line 400 400 800 800))
.

now run:
djvused myfile.djvu -f annotations.dsed -s

and view your file in DjView 4.6