1. Open a file (the user running the web server must have read access to the file).
2. Read the file contents into a variable.
3. Close the file.
4. Get the file size.
5. Set the HTTP headers properly.
6. Send the variable contents to the browser.

my $downloadfile = $query->param('downloadfile');
my $fullpathdownloadfile = "$fullpath/$downloadfile";
my $output = '';
my $buffer = '';
open my $fh, '<', $fullpathdownloadfile
  or return error_handler("Error: Failed to download file <b>$downloadfile</b>:<br>$!<br>");

while (my $bytesread = read($fh, $buffer, 1024)) {
  $output .= $buffer;
}

close $fh
  or return error_handler("Error: Failed to download file <b>$downloadfile<b>:<br>$!<br>");

my  $downloadfilesize = (stat($fullpathdownloadfile))[7]
  or return error_handler("Error: Failed to get file size for <b>$downloadfile<b>:<br>$!<br>");

$self->header_props(
                    '-type'                => 'application/x-download',
                    '-content-disposition' => "attachment;filename=$downloadfile",
                    '-content_length'      => $downloadfilesize,
                   );

return $output;

• downloadapp.pl, the application wrapper
• DownloadApp.pm, the application module
• downloadapp1.tmpl.html, the 1st screen's HTML template
• downloadapp2.tmpl.html, the 2nd screen's HTML template