PHP: Serve a file for download without providing the direct link
<p>I want to serve invoices for download. Currently I'm using a simple numbering scheme (invoice-01.pdf, invoice-02.pdf, and so on). I know that I could use hashes instead to obscure the data.</p>

<p>Is it also possible to use PHP and serve the invoices by not directly having the user point to them?</p>
