Renaming files in one shot

[Vittorio]

Under a directory I have many pdf files named according to M$ Windows 
rules, that is:

Marylin Monroe.pdf
James Stewart.pdf
Alice in 
Wonderland.pdf
Ludwig Van Beethoven.pdf
.....
.....

Now I'd like to 
rename them ** IN ONE SHOT ** (some more steps would be acceptable 
anyway!) deleting all the blanks, that is

MarylinMonroe.pdf
JamesStewart.pdf
AliceinWonderland.pdf
LudwigVanBeethoven.pdf
........
........

How can I do that?

Ciao
Vittorio