my $filename = "whatever...";
{
    open( my $fh, "<", $filename ) or die "$filename: $!";
    local $/ = "</PC-Compound>";

    while (<$fh>) {   # read one entire PC-Compound block
        next unless ( m{\w\s*</PC-CompoundType_id_cid} and
                      m{\w\s*</PC-InfoData_value_binary} );

        s/^.*?(?=<PC-Compound)//;  # remove anything that precedes the block
        process_compound( $_ );
    }
}