How to send a local file and expect other file?

I'm trying to make a simple web call work in command line mode and what I would like to do is:

1. send a document file to http://domain.com/convert/
2. receive as the response a PDF file

I can see that I can't send a file using curl and download other using the same call, so I was trying to make 2 calls where in the first send I would get an unique identifier that would be used to retrieve the PDF file on the second call.

For example:

@echo off
set var = curl --form upload=@localfilename http://domain.com/send-file.ashx
echo The Unique Identifier is "%var%"
curl http://domain.com/get-file.ashx?id=%var% -O "newfile.pdf"

But I'm getting error upon creating the file:

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
Warning: Failed to create the file
Warning: get-file.ashx?id=00000000-0000-0000-0000-000000000000
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
curl: (23) Failed writing body (0 != 1132)

It seems that it does not care about newfile.pdf and tries to create the file using the same name of the web page...

How would I change my script in order to work?