Upload a file inside a JS FormData object through PHP using fetch

I’m sending a FomData object using fetch, that contains all my form elements, including a PDF file to upload. I am successfully receiving the data in my PHP file but, How can I upload the file from the FormData object?

my JS file:

//extracts all data from my Form
const formD = new FormData($(this)[0]);
var object = {};
formD.forEach((value, key) => object[key] = value);

//sends data to the php file
fetch('/modules/editData.data.php', {
method: "POST",
headers: {
"Content-Type": "application/json; charset=UTF-8"
},
body: JSON.stringify(object)
})
.then(res => res.json())
.then(data => console.log(data));
}  
});

my PHP file:

$json = file_get_contents('php://input');
$data = json_decode($json);

$fileID  = $data->fileID;
$name    = $data->name;
$file    = ???? 

I have tried

if(isset($_FILES['files'])) {
    echo json_encode('OK');
}

but no results where obtain. The rest of the data from the form is fine, I just need to know how to obtain the file from the FormData to use PHP move_uploaded_file