PDF in Website: Download via Ajax

I'm writing a complex WebApplication and run into some problems. I hope you can help me out here...

I'm generating some PDF files on my server. To generate these PDF files, I first need to POST a form via AJAX (JSON), so the server has all required information to generate the PDF. But the server (i'm using Spring MVC) should not save the PDF but instead return it immediately to the client.

That means the response of the POST request would be the PDF file already. How can i display this PDF file in the Browser? I would like to use a library for displaying PDFs, so i get more control over the PDF-Viewer (want to use custom toolbars). I was thinking about using pdf.js for that.

The Ajax POST is quite huge so i cannot use a GET request with URL parameters.

Any ideas? Thanks very much for any help!