How to prevent automatic file donwload when we insert blob to iframe element but iframe cannot display?

Question

In my MVC project,

I have a file upload page. In this page, I want to preview files. When a file inserted into my file input element, I send this file to my controller(named: "FilesController") and i try to get this file if it is pdf or not. If this file is not pdf so i convert it to pdf and resend to view with AJAX. the whole process is run with ajax. There is no page refreshing.

The problem is, sometimes when i upload CSV file, This file goes to server and server tries to convert it to PDF byte array and finally sends to View. In view, I try to convert this byte array as base64 and convert to buffer array. and Finally I create blob. I insert this blob to FilePreview iframe element and try to show file.

Like I said, CSV does not work. But It works with PDF PNG. I understand this problem, sometimes server converts pdfs badly. So my willing is simple. If it is a malformed PDF, I won't show it to iframe.

How can I do this?

Here is my ajax code:

`

function ConvertFilesToBytes(files) {
            //if (files.length > 0) {
            var formData = new FormData();
            formData.append("file", files);
            $.ajax({
                method: "POST",
                url: "/FileManagement/PreviewFileFromBytes",
                processData: false,
                contentType: false,
                data: formData,
                beforeSend: function () {
                    $("#FilePreviewFrame").text("Ön izleme getiriliyor... Lütfen Bekleyiniz ...");
                },
                success: function (res) {

                    var bufferedBytes = _base64ToArrayBuffer(res.fileBytes);
                    var blob = new Blob([bufferedBytes], { type: res.fileContentType });
                    var url = URL.createObjectURL(blob);
                    $("#FilePreviewFrame").attr('src', url);
                    $("#FilePreviewFrame").addClass('border border-info ');

                    //SetFilesToFrame(res);
                },
                error: function (xhr) {
                    log("Ön izleme oluşturulamadı!", "red");
                }
            });
        }

`

Here is my buffer array converter:

`

function _base64ToArrayBuffer(base64) {

    var binary_string = window.atob(base64);
    var len = binary_string.length;
    var bytes = new Uint8Array(len);
    for (var i = 0; i < len; i++) {
        bytes[i] = binary_string.charCodeAt(i);
    }
    return bytes.buffer;
}

`

Note: I do not need show all types of files. I need to show wellformed files. But when it comes malformed file, I want to prevent showing into iframe.

So

1. Can we prevent IFRAME to not download file?
2. Can we detect malformed PDF?

If 1 or 2, This question will be successed :) ...

I did not found any response from google or stackoverflow.

I look at here: how to prevent download when the pdf load to iframe? iframe - prevent it from downloading anything