In modern browsers, you can use a Blob to create an object URL which can then be used instead of a base64 URL (which has some limitations in different browsers, like length limits).

Here's a working example that does that. This sample displays the PDF inside an iframe, but you can really do whatever you want with that objectURL like open it in a new tab or whatever.

var xhr = new XMLHttpRequest();
xhr.responseType = 'arraybuffer';
xhr.onload = function() {
    // Create the Blob URL:
    var buffer = xhr.response;
    var blob = new Blob([buffer], {
        type: 'application/pdf'
    });
    var objectURL = URL.createObjectURL(blob);

    // Create an iframe to demonstrate it:
    var iframe = document.createElement('iframe');
    iframe.className = 'sample-iframe';
    iframe.src = objectURL;
    document.body.appendChild(iframe);
    console.log(objectURL);
};
xhr.open('GET', 'https://gist.githubusercontent.com/AlexanderOMara/4cd0ae77a3027a8363eecb5929b30ee3/raw/900734831709f3cb94718649ca8f7f9715adeb78/hello-world.pdf', true);
xhr.send();

html, body {
  width: 100%;
  height: 100%;
}  
.sample-iframe {
  width: 90%;
  height: 90%;
}

Of course, the browser's built-in print function for the PDF will work also.

If you already have the byte[], you should use FileContentResult, which "sends the contents of a binary file to the response". Only use FileStreamResult when you have a stream open.

public ActionResult DisplayPDF()
{
    byte[] byteArray = GetPdfFromDB();

    return new FileContentResult(byteArray, "application/pdf");
}

1. Download the binary data with ajax, into an arraybuffer

var xhr = new XMLHttpRequest;
xhr.open('get', '/path/to/pdf', true);
xhr.responseType = 'arraybuffer';
xhr.send();

2. Create Blob and Object URL

var blob = new Blob([xhr.response], {type: 'application/pdf'});
var url = URL.createObjectURL(blob);

3. Load URL in iframe

iframe.src = url;

Demo: https://webblocks.nl/tests/ajax-pdf.html

I would recommend creating another action on the controller designed specifically for rendering the PDF data. Then it's just a matter of referencing it within your data attribute:

data="@Url.Action("GetPdf", "PDF")"

I'm not sure you can dump raw PDF data within the DOM without hitting some kind of encoding issue. You may be able to do like images, though I've never tried. But, for demo's sake and image would look like:

src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7"

So, assuming the same could be done it would probably look like the following:

@{
  String base64EncodedPdf = System.Convert.ToBase64String(Model.pdfInBytes);
}

@* ... *@
<object data="data:application/pdf;base64,@base64EncodedPdf"
        width="900" height="600" type="application/pdf"></object>

I still stand by my original response to create a new action however.

The data attribute of the object tag should contain a URL which points to an endpoint which will provide the PDF byte stream. It should not contain the byte stream itself inline.

To make this page work, you will need to add an additional handler that provides the byte stream, e.g. GetPdf.ashx. The ProcessRequest method of the handler would prepare the PDF bytestream and return it inline in the response, preceded by the appropriate headers indicating it is a PDF object.

protected void ProcessRequest(HttpContext context)
{
    byte[] pdfBytes = GetPdfBytes(); //This is where you should be calling the appropriate APIs to get the PDF as a stream of bytes
    var response = context.Response;
    response.ClearContent();
    response.ContentType = "application/pdf";
    response.AddHeader("Content-Disposition", "inline");
    response.AddHeader("Content-Length", pdfBytes.Length.ToString());
    response.BinaryWrite(pdfBytes); 
    response.End();
}

Meanwhile your main page would populate the data attibute with a URL pointing at the the handler, e.g.

objTag.Attributes["data"] = "GetPdf.ashx";

This works for me on Chrome, but not on IE:

// base64DataFromWebAPI comes from a Web API, in the form of base 64 string
var pdfData = base64DataFromWebAPI;

var x = window.open();
var iframe = x.document.createElement('iframe')
iframe.width = '100%'
iframe.height = '100%'
iframe.frameBorder = 0
iframe.style = "border: 0"
iframe.src = "data:application/pdf;base64, " + pdfData
x.document.body.appendChild(iframe);

I got it from the following Stack Oveflow question: JsPDF - Not allowed to navigate top frame to data URL

I tried this in jsFiddle, and it works well in Chrome & FF, need to check on other browsers as well.

Convert the byte[] to Base64 using,

string base64PDF = System.Convert.ToBase64String(outputPDF, 0, outputPDF.Length);

All I had to do is specify the MIME type as data:application/pdf;base64, in the source and give the Base64 version of the PDF.

<object data="data:application/pdf;base64, JVBERi0xLjQKJeLjz9MKMyA..." type="application/pdf" width="160px">
    <embed src="data:application/pdf;base64, JVBERi0xLjQKJeLjz9MKMyA..." type="application/pdf" />
</object>

I couldn't be able to hide the top toolbar which appears in FF by appending #toolbar=0&navpanes=0&statusbar=0.

IE8 needs a saved pdf file to be displayed.