#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my @parts;
my $index = 0;

open my $fh, '<', 'test.txt' or die $!;
while ( my $line = <$fh> ) {
    if ( $line =~ /Wichtiger Teil\s+(\d+)/ ) {
        $index = $1;
    }

    if ( $line =~ /^ =+ \s Wichtiger \s+ Teil/x .. $line =~ /^=+ \s+ Ende \s+ =+/x ) {
        $parts[$index] .= $line;
    }
}

close $fh;

warn Dumper \@parts;