bash - How do I move files from many child directories into my root directory?

I'm using bash on Mac 10.9.5. I have PDF files in many directories, all one level from the root ...

Dir_1/abc.PDF
Dir_2/def.PDF
Dir_3/ghi.PDF
Dir_3/jkl.PDF
...

How do I write a shell command to move all these files into the "root" directory, that is make the files line up alongside the child directories ...

abc.PDF

def.PDF
ghi.PDF
Dir_1
Dir_2
Dir_3

?

Answer

How about just:

mv ./*/*.pdf .

I've done a test on my computer (zsh 5.0.7 (x86_64-pc-linux-gnu)) and it worked perfectly:

> ls -r *    

sub3:
r.2  r.1


sub2:
s.2  s.1

sub1:
t.2  t.1

> mv ./*/*.pdf .
> ls
r.1  r.2  s.1  s.2  sub1  sub2  sub3  t.1  t.2



> tree                                                            
.
├── r.1
├── r.2
├── s.1
├── s.2
├── sub1
├── sub2

├── sub3
├── t.1
└── t.2