jquery - handle posted formData object with files and other inputs in php

I need to handle inputs from form post and I have no idea, how to do it in php, because when I write for example $_POST["header"], it var_dumps null.

I am creating formData object and inserting all inputs from form. Then posting it with ajax.

Can you please help me? I need to handle "header", "content", "password" and files.

<form method="post" enctype="multipart/form-data" id="uploadFiles">
    <label for="newsHeader" id="headerLabel">Nadpis</label>
    <input type="text" name="newsHeader" id="newsHeader">
    <label for="content" id="contentLabel">Text novinky</label>
    <textarea name="content" id="content"></textarea>
    <label for="files" id="filesLabel">Fotky</label>
    <input type="file" name="files" id="files" accept="image/jpeg" multiple>
    <label for="password" id="passwordLabel">Heslo pro upload</label>
    <input type="text" name="password" id="password">
    <button type='submit' id='uploadFilesSubmit'>NAHR??T</button>
</form>



$("#uploadFiles").submit(function(event){
        event.preventDefault();
        var formDataObj = new FormData(),
        header = $("#newsHeader").val(),
        content = $("#content").val(),
        password = $("#password").val();

        formDataObj.append("header", header);
        formDataObj.append("content", content);
        formDataObj.append("password", password);
        $.each($("#files")[0].files, function(i, file) {
            formDataObj.append('file', file);
        });

        console.log(Array.from(formDataObj));


        $("#uploadFilesSubmit").html("<div class='buttonSubmitIcon'><i class='fas fa-sync'></i></div>");
        $.ajax({
            method: "POST",
            url: "uploadNews.php",
            data: {
                formDataObj: formDataObj
            },
            dataType: 'json',
            contentType: false,
            processData: false,
            success: function(results){

            }, error: function(){

            }

        });


    });
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In uploadNews.php I have this:

exit(json_encode(var_dump($_POST["header"])));
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It always returns "Undefined index: header", same as content or count($_FILES["file"]["name"])

All I want is to get somehow to posted values.. Thank you very much