See perlop about quotes. Single quotes perform no variable expansion. Double quotes do. Since you are already using double quotes inside of your string, you might want to use qq{} or sprintf or, as you do at the top of your script, HTML::Template to perform the variable substitution:

print qq{<input type="button" value="Download PDF Report" onClick=$lin
+k, $download); return false;">};

# or

printf '<input type="button" value="Download PDF Report" onClick=%s, %
+s); return false;">', $link, $download;
[download]