Usage is a little convoluted... You'll need 'pdfcrack' (http://pdfcrack.sourceforge.net/ or apt-get install pdfcrack) first.

Run pdfcrack on your PDF file, then stop it before it starts cracking the password:

$ pdfcrack pdfs/Untitled1_UserPw-oZ4r.pdf 
PDF version 1.4
Security Handler: Standard
V: 2
R: 3
P: -1028
Length: 128
Encrypted Metadata: True
FileID: 1e9a3e73564cc53d6f6b3c328cb9d44b
U: bed6172072e7401a65c3bb5cb5bd87dc00000000000000000000000000000000
O: 4d5d94faf81719e50b1195c59543fd5cde9d2158ca622be4de609bd15682dad1

<CTRL-C>

Now you need to combine the values in the form:

./cudapdf P Length FileID U O

e.g. for the example above:
./cudapdf -1028 128 1e9a3e73564cc53d6f6b3c328cb9d44b bed6172072e7401a65c3bb5cb5bd87dc00000000000000000000000000000000 4d5d94faf81719e50b1195c59543fd5cde9d2158ca622be4de609bd15682dad1

The password for the hash set above is "oZ4r".