4.6mb??
Think you friend tried to save the file in colour. Try to do it "Black and White" and that will reduce the size of the file considerably. Also, most likely he will be doing it in an A4 size scanner. If the licence size is smaller than A4, he can cut the the scanned area to fit just the size of the licence, hence, reducing the size of the file.
Also, as Alatnariver mentions, reducing the quality of the scan reduces the size of the file (if 300 dpi works out in a heavy file, try 200 dpi or 150 dpi, etc)
"Trial and error" is the name of the game.
Best of luck,
Zero