Untested code coming...

#!/usr/bin/perl

my $pattern = "PGP";

&renameFiles('/home/user/perl/testincoming');

sub renameFiles {
    # Pass directory name as parameter
    my $Dir = shift;

    opendir(DIR, $Dir) || die "Can't opendir $Dir: $!";
    my @Files = grep { -f "$Dir/$_" } readdir(DIR);
    rewinddir(DIR);
    my @Dirs = grep { /^[^.].*/ && -d "$Dir/$_" && ! -l "$Dir/$_"} rea
+ddir(DIR);
    closedir DIR;

    foreach $file (@Files) {
        open(FILE,"<$Dir/$file") || die "Can't open $file: $!";
        my $doRename=0;
        READFILE: while (<FILE>) {
            if (/\Q$pattern\E/) {
                $doRename=1;
                last READFILE;
            }
        }    
        close(FILE);
                if ($doRename) {
            my $newname=$file;
                    $newname=~s/^./o/;
                    rename ("$Dir/$file", "$Dir/$newname");
        }
    }

    # Call self for each subdir    
    foreach $SubDir (@Dirs) { &renameFiles(join("/",$Dir,$SubDir)); }
};
[download]

Should rename all files containing a PGP line in the whole subdirectory tree. This is just a quick modify of something I already had, so it may contain bugs, etc...
I'm not responsible for what it does to your system, no warraty, etc, etc. You know the standard phrases.

UPDATE:As merlyn humbly suggests in his post, I now check for symlinks with && ! -l "$Dir/$_". The code is still untested from my part.

/brother t0mas