How to read formdata and json data in c# .net

Question

I want to read json data and formdata(attachments) in my C# method from the ajax call. Need to upload the files and some json data. Unable to get the values from the ajax in my C# method.

JS Code :

function FileUploadd() {

    var lang = $("ul.nav-tabs li.active a")[counterF - 1].text;
    $("ul.nav-tabs li.active a").each(function() {
        if (this.hash == paneId)
            lang = this.innerText;
    });
    var jsonObjects = JSON.stringify({
        'QuestionNumber': 1,
        'Language': "amit",
        'Countries': "C1",
        'Attachments': attchmt
    });
    // Checking whether FormData is available in browser
    if (window.FormData !== undefined) {
        var fileUpload = $("#FileUpload" + qnNo).get(0);
        debugger;
        var files = fileUpload.files;
        // Create FormData object
        var fileData = new FormData();
        // Looping over all files and add it to FormData object
        for (var i = 0; i < files.length; i++) {
            var newFile = 'Q' + qnNo + '_' + lang;
            //fileData.append(files[i].name, files[i]);
            files[i].Filename = newFile;
            fileData.append(newFile, files[i]);


        }
        $.ajax({
            url: '/RequirementManagement/FilesUpload',
            type: "POST",
            contentType: false, // Not to set any content header
            processData: false, // Not to process data
            data: {
                fObj: jsonObjects,
                fd: fileData
            },
            success: function(result) {

            },
            error: function(err) {
                alert(err.statusText);
            }
        });
    } else {
        alert("FormData is not supported.");
    }
};

C# Code:

public void UploadTestForm(JsonModel fObj, FormData fd)
{
  //Code here 
} 

JsonModel is my model class and not sure what will the datatype to receive formdata. Don't know how start and proceed.