Add direct download link in user mail settings.

You can use PHP script for you to auto download the pdf file.
Link:

$pdf_link = add_query_arg(
                    array(
                "action" => "pdf_download",
                "file" => $fname . ".pdf",
                "_wpnonce" => wp_create_nonce("security-code-for-your-file-download")
                    ), admin_url("admin-post.php"));

<a href="$pdf_link">Download PDF</a>

Function:

public static function pdf_download(){

            $fullPath = WP_PLUGIN_DIR."/".$_GET['file'];
            $fsize = filesize($fullPath);
            $path_parts = pathinfo($fullPath);
            // We'll be outputting a PDF
            header('Content-type: application/pdf');
            // It will be called downloaded.pdf
            header('Content-Disposition: attachment; filename="'.$path_parts["basename"].'"');
            header("Content-length: $fsize");
            header("Cache-control: private"); //use this to open files directly
            readfile($fullPath);
            exit;
        }

Hope it helps.

How did you create your pdf and anchor link for email?

Can I see your code? where you setup the link for email?

My Code above ex.:

link code – is use for creating link url for the anchor tag
function code – is the function that will receive the link for download

Also I forget to add this. Sorry.
//hooks up download action
add_action(“admin_post_pdf_download”, “pdf_download”);

ah okay, I was thinking that you did automatically create you pdf using php and email directly to recipient.

The easiest way to do that is to install download manager plugin Link then copy the embed code of the specific file you want to be downloaded.

That’s it hope I did solved your problem.