my $output_directory="TEMPORARY";

sub open_directory_file
{
print "Open files from directory...\n";
my @all_file_contents;

#added following line
my $pwd = cwd();

my $Directory = File::Spec->canonpath( $mw->chooseDirectory() );
my $shortpath = Win32::GetShortPathName( "$Directory" );
chdir($shortpath) or die "$!";

opendir (DIR, "$shortpath") or die "$!";
my @files = grep {/.*?\.txt/}  readdir DIR;
close DIR;

#added following line
#go back to original directory
chdir($pwd);
}