add appearance image to top left corner of a page how can i do that?
The Stamper class is idea for this, as regardless of the page specifics, Stamper will calculate the top left corner, and place your annotation there.
So what you can do is use Stamper to add an annotation, and get that annotation. See this post.
Then call
Rect annot_rect = stamp_annot.GetRect();
page.RemoveAnnot(stamp_annot);
Then you can use annot_rect to create your signature widget.