Parse multipart/form-data response in rust / reqwest - pdf

Question

I'm relatively new to rust and using reqwest to fetch a PDF document from a REST API endpoint. The content-type of the response is multipart/form-data; boundary=bc1f6465-6738-4b46-9d9d-b9ae36afa8cb with two parts:
--bc1f6465-6738-4b46-9d9d-b9ae36afa8cb
Content-Disposition: form-data; name="metadata"
Content-Type: application/json
{"documentId":"QkNfRENfSUwwMDEsRTA1OEU3ODQtMDAwMC1DNzY5LTg1MjktMTRFRkI5RTBFNjRF"}
--bc1f6465-6738-4b46-9d9d-b9ae36afa8cb
Content-Disposition: form-data; name="document"; filename=document.pdf
Content-Type: application/pdf
%PDF-1.4
<binary content>
%%EOF
--bc1f6465-6738-4b46-9d9d-b9ae36afa8cb--
I want now to save the PDF document in the 2nd part as a valid PDF file on disk. But the multipart functionality within reqwest seems to create new multipart requests whereas I need to parse a multipart response.
My code to download the file:
use reqwest::{self, header::AUTHORIZATION};
fn main() {
let url = "https://example.com/rest/document/123";
let authorization_header = String::from("Bearer ") + access_token.as_str();
let res = client.get(url)
.header(AUTHORIZATION, &authorization_header)
.send()
.expect("Error calling API");
}
Any hint on how to process the multipart/form-data response is appreciated!