my $src_qfn = 'BulletinV3, 1 Montana 20xx-xx-xx (print).pdf_FN_TEMPLATE';

if (-e $src_qfn) {
   ...
} else {
   ...
}

##</code><code>##

my $src_qfn = 'BulletinV3, 1 Montana 20xx-xx-xx (print).pdf_FN_TEMPLATE';

if ( stat( $src_qfn ) ) {
   ...
} else {
   die( "Can't stat `$src_qfn`: $!\n" ) if !$!{ ENOENT };
   ...
}

##</code><code>##

system( "zenity",
   "--title" => "Rename problem",
   "--width" => 400,
   "--error",
   "--text"  => "Can't rename `$src_qfn` to `$dst_qfn`: $!",
)