print "Content-Type: application/octet-stream\n\n";
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After all, how can you have two Content-Type header? If what you have is a plain text file to send, you don't need that octet-stream. I think you want,

print "Content-Type: text/plain\n";
print "Content-Length: $filesize\n";
print "Content-disposition: attachment; filename=$filename\n\n";

open FILE, $filename or die "can't open $filename: $!\n";
print while <FILE>;
close FILE;
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use CGI::Simple;
use strict;
use warnings;

my $cgi = CGI::Simple->new;
my $filename = '/usr/local/..../file.txt'; # assumed exists

print $cgi->header(
  -type => 'text/plain',
  -attachment => $filename,
  -content_length => -s($filename),
);

open FILE, $filename or die "Can't open $filename: $!\n";
print while <FILE>;
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sub downloadFile {
    # $filepath is the directory
    # $filename is the name of the file
    my ($filepath,$filename) = @_;
    chdir($filepath) || return(0);
    my $filesize = -s $filename;
    # print full header
    print "Content-Type: application/octet-stream\n\n";
    print "Content-Length: $filesize\n";
    print "Content-disposition: attachment; filename=$filename\n\n";
    print "Content-type: text/plain\n\n";
    # open in binmode
    open(READ,$filename) || die;
    binmode READ;
    # stream it out
    binmode STDOUT;
    while (<READ>) {
        print;
    }
    close(READ);
    # should always return true
    return(1);
}
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Also, you are sending two Content-Type headers for the same data. text/plain would probably be appropriate for the dbschema.txt file.

binmode() is also probably unnecessary.

-David

telnet localhost 80
GET /theurl
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