for that - what a Gem
I probably clicked on Add Books a couple of times when I first got Calibre, but its not even in my tool bars today.
I use the command line to create empty books and then drop the format files into the empty book - it suits me better do it that way.
Being able to add arbitrary files to a book creates some interesting possibilities. My only wish would be that the File Type selector would use the 'same as last time'.
Thanks again Kovid
BR