-----------------8<---------8<------------------
use strict;
use warnings;

    my  $filename = 'tablet2.data1.txt';
    open( IN, "<$filename" )
        or  die "Unable to open input file '$filename': $!";

    local   $/ = undef;
    my  $buf  = <IN>;
    
    my  $pattern = 'The text to be searched\s*in differnt lines inclunding\s*white lines and indentation\s*';
    my  $replace = <<'EOF';
  It seems like 
      magic
but it's really just waving wands 'n stuff
EOF
    $buf =~ s/$pattern/$replace/;
    print $buf;
    close(IN);

-----------------8<---------8<------------------
use strict;
use warnings;
use Tie::File; 

# tie @array to filename using Tie::File 
tie my @array, 'Tie::File', 'result.txt' 
    or die "Cannot open result.txt:$!"; 
#while( <result.txt> ) { 
    for(@array) { 
        my $pattern = "The text to be searched in differnt lines inclunding white lines and indentation"; 
        my $replace = " The replacing text also in multiple lines including white spaces and white lines "; 
        $pattern = '\s\s';
        $replace = '||';
        s/$pattern/$replace/g; 
    } 
#} 
untie @array;