This article is from the PGP FAQ, by Jeff Licquia email@example.com with numerous contributions by others.
No. The reason for this is that the signature contains information
(called a "message digest" or a "one-way hash") about the message it's
signing. When the signature check is made, the message digest from
the message is calculated and compared with the one stored in the
encrypted signature block. If they don't match, PGP reports that the
signature is bad.