Newbie... Verifying a p7s signature

[Keith Hyland]

Hi,

I a complete newbie to using gpg..

I've got a sample detached signature  which I would like to verify.

Its in a p7s format (I don't know what this means)... I also have the
original pdf docuemnt that was signed.

When I try to verfiy it I get ..
gpg -v --verify doc.pdf.p7s doc.pdf
gpg: no valid OpenPGP data found.
gpg: the signature could not be verified.
Please remember that the signature file (.sig or .asc)
should be the first file given on the command line.

Anybody got any ideas? Do I need the public key or is it included in the 
p7s file?

Cheers,
Keith