use strict;
use warnings;

open my $inFH, q{<}, \ <<'EOD' or die qq{open: << HEREDOC: $!\n};
1,XYZ,desc,PDF
2,YGH,desc,KMN
1,XYZ,desc,QFZ
EOD

my %ids;
while ( <$inFH> )
{
    chomp;
    my ( $key, $value ) = m{^(.*,)(.*)$};
    push @{ $ids{ $key } }, $value;
}

print qq{$_@{ [ join q{,}, @{ $ids{ $_ } } ] }\n}
   for keys %ids;

close $inFH or die qq{close: << HEREDOC: $!\n};