Путь разработчика

function addFileUploadBox()
{
    if (!document.getElementById || !document.createElement)
        return false;
 
    var uploadArea = document.getElementById ("upload-area");
 
    if (!uploadArea)
        return;
 
    var newLine = document.createElement ("br");
    uploadArea.appendChild (newLine);
 
    var newUploadBox = document.createElement ("input");
 
    // Set up the new input for file uploads
    newUploadBox.type = "file";
    newUploadBox.size = "50";
 
    // The new box needs a name and an ID
    if (!addFileUploadBox.lastAssignedId)
        addFileUploadBox.lastAssignedId = 100;
 
    newUploadBox.setAttribute ("id", "dynamic" + addFileUploadBox.lastAssignedId);
    newUploadBox.setAttribute ("name", "dynamic:" + addFileUploadBox.lastAssignedId);
    uploadArea.appendChild (newUploadBox);
    addFileUploadBox.lastAssignedId++;
}

        HttpFileCollection uploads = HttpContext.Current.Request.Files;
        for (int i = 0; i < uploads.Count; i++)
        {
            string fileName = uploads[i].FileName;
            //обрабатываем файл
        }