Error attachment

Hi, I created a form with attachment but the emails I receive is as follows. Why?

Rispondi a: [email protected]
MIME-Version: 1.0
Content-Type: multipart/mixed;
	boundary="b1_42ffeb98afc2139c18f5a696d0249789"
Content-Transfer-Encoding: 8bit

This is a multi-part message in MIME format.

--b1_42ffeb98afc2139c18f5a696d0249789
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Da: test test <[email protected]>
Oggetto: test

Corpo del messaggio:
test

--
Questa e-mail è stata inviata da un modulo di contatto su Wispa Italia (http://www.wispaitalia.com)

--b1_42ffeb98afc2139c18f5a696d0249789
Content-Type: application/pdf; name="nuova_composizione.pdf"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=nuova_composizione.pdf

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...
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