Pdf missing signature after uploading from ASP.NET MVC XMLHttpRequest - asp.net-mvc

Question

I'm working on a ASP.NET MVC page to let users upload a Pdf document once they have digitally signed it.
But for some reason the signature is destroyed when uploading the document even when it's graphic representation is properly displayed.
Here is the code I use to upload the file:
$(document).on('click', 'input[value=Upload]', function (e, argument) {
var formdata = new FormData();
for (i = 0; i < document.getElementById('FileBox').files.length; i++) {
formdata.append(document.getElementById('FileBox').files[i].name, document.getElementById('FileBox').files[i]);
}
var url = '#Url.Action("Upload", "Test")'
var xhr = new XMLHttpRequest();
xhr.open('POST', url);
xhr.send(formdata);
xhr.onreadystatechange = function () {
if (xhr.readyState == 4 && xhr.status == 200) {
var response = $.parseJSON(xhr.response);
alert(response.result);
}
}
});
I'm retrieving the uploaded files in the controller as follows:
Public Function PostedFiles() As List(Of Byte())
Dim retval As New List(Of Byte())
Dim oRequest As HttpRequest = Web.HttpContext.Current.Request
For Each sFileKey As String In oRequest.Files
Dim oFile As HttpPostedFile = oRequest.Files(sFileKey)
If oFile.ContentLength > 0 Then
Dim iLength As Integer = oFile.ContentLength
Dim oBytes(iLength) As Byte
Dim oStream As System.IO.Stream = oFile.InputStream()
oStream.Read(oBytes, 0, iLength)
retval.Add(oBytes)
End If
Next
Return retval
End Function
After persisting the byte arrays in a SQL server database, when I take them back from the database there is no longer any signature, just the graphic representation of it.

Answer 1

Thanks Mkl for your comment, I realize I was getting no signature since the document was displayed in the browser. Opening the persisted file in Acrobat Reader successfully shows the signature.