Well, I don't know if this is the whole problem, but you're doing a lot of unnecessary work. If you want to read a complete file into a scalar, then print it, you can do it all in one go:

binmode XLS;
{
    print header(-type => 'application/vnd.ms-excel');
    local $/;
    print <XLS>;
    close XLS;
}
[download]

The same applies to your PDF file.

HTH