How To Receive PDF by webservice through HTTP POST

Hi to Everybody. First of all sorry for my English, but I don't write in english very soon....
I need help about requesting a .pdf file (for example the stamp of a Sales Invoice) from NAV and receiving it by the webservice through HTTP POST.
I have already written the code to send the request to the webservice like this:

CREATE(locautoHTTPPOST);
locautoHTTPPOST.Open('POST','https://www.g*****way.it/g*******new/ricercadocumentipost.aspx');
Testo := 'CodiceLicenza' + '=' + 'G00*****' +
'&' + 'CodiceAziendaSIA' + '=' + 'P***P' +
'&' + 'Nickname' + '=' + 'webservice' +
'&' + 'Password' + '=' + '6******3' +
'&' + 'CodiceGrafica' + '=' + 'F' +
'&' + 'NomeCampoRicerca' + '=' + 'G0000371_CAMPO2' +
'&' + 'ValoreCampoRicercaa' + '=' + 'VB09-00001';
locautoHTTPPOST.Send(Testo);


locautoHTTPPOST is ean AUTOMATION of Microsoft WinHTTP Services
Testo is a Text Variable in wich i store some values of the document i want to receive form the webservice (written following the vendor of the webservice guidelines)

Now that i have sended the request I expect the webservice to respond sending the pdf, but i don't know how to receive it, and see it or save it in a file...

Could you help me in some way?
Thanks to all of you!!!