Uploading Files in ASP.net without using the FileUpload server control

In your aspx :

<form id="form1" runat="server" enctype="multipart/form-data">
 <input type="file" id="myFile" name="myFile" />
 <asp:Button runat="server" ID="btnUpload" OnClick="btnUploadClick" Text="Upload" />
</form>

In code behind :

protected void btnUploadClick(object sender, EventArgs e)
{
    HttpPostedFile file = Request.Files["myFile"];

    //check file was submitted
    if (file != null && file.ContentLength > 0)
    {
        string fname = Path.GetFileName(file.FileName);
        file.SaveAs(Server.MapPath(Path.Combine("~/App_Data/", fname)));
    }
}

Here is a solution without relying on any server-side control, just like OP has described in the question.

Client side HTML code:

<form action="upload.aspx" method="post" enctype="multipart/form-data">
    <input type="file" name="UploadedFile" />
</form>

Page_Load method of upload.aspx :

if(Request.Files["UploadedFile"] != null)
{
    HttpPostedFile MyFile = Request.Files["UploadedFile"];
    //Setting location to upload files
    string TargetLocation = Server.MapPath("~/Files/");
    try
    {
        if (MyFile.ContentLength > 0)
        {
            //Determining file name. You can format it as you wish.
            string FileName = MyFile.FileName;
            //Determining file size.
            int FileSize = MyFile.ContentLength;
            //Creating a byte array corresponding to file size.
            byte[] FileByteArray = new byte[FileSize];
            //Posted file is being pushed into byte array.
            MyFile.InputStream.Read(FileByteArray, 0, FileSize);
            //Uploading properly formatted file to server.
            MyFile.SaveAs(TargetLocation + FileName);
        }
    }
    catch(Exception BlueScreen)
    {
        //Handle errors
    }
}

You'll have to set the enctype attribute of the form to multipart/form-data; then you can access the uploaded file using the HttpRequest.Files collection.