The frame of my conservatory door is not quite square at present, and the
hinges don't offer enough adjustment to compensate. I would like to lower
one corner of the door frame, but I can't figure out how it's held in place.

I lifted the doors off their hinges, removed the masonry fixings between the
door frame and the dwarf walls, and removed the spacers between the door
sill and the bricks underneath the door. There is some space between the
door sill and the bricks, so it ought to be possible to lower the door
frame, but even when I jumped up and down on the door frame, it didn't drop
at all.
There no other visible fixings in the door frame or the adjacent window
frames that could be holding it in place, so what's supporting it?
There are some vertical trim strips between the door and window frames, but
I think I'd need to remove part of the roof to slide them out, so hopefully
that won't be necessary.

Here are some pictures:

http://i26.tinypic.com/13zsuap.jpg
http://i32.tinypic.com/2z50j1v.jpg
http://i25.tinypic.com/o580b7.jpg