Open file in mvc3 on click of button

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Javascript

MVC3

I have one button on my partial view,I want to open pdf file on click of button

<button type="button" class="CleanButton" name="button" onclick="ValidateFaxReports('/Verification/PreviewFax','faxReportsComments','FaxReports');">
                           Preview Fax
                       </button>

Onclick of the button I need to call javascript function, to check some validation,
'/Verification/PreviewFax' is Url, faxReportsComments is my form Id, FaxReports is id of div which I am using in main view.
Here is my function

private string ViewReport(string file)
        {
            string errorMessage = string.Empty;
            byte[] buffer = null;
            try
            {
                if (file.ToLower().Contains(".enc"))
                {
                    buffer = VOEI.DAL.Crypto.DecryptBinaryFileToByteArray(file);
                    file = file.ToLower().Replace(".enc", String.Empty);
                }
                else
                {
                    FileStream fs = new FileStream(file, FileMode.Open, FileAccess.Read, FileShare.Read);
                    BinaryReader binReader = new BinaryReader(fs);

                    buffer = binReader.ReadBytes((int)fs.Length);
                    binReader.Close();
                    fs.Close();
                }
            }
            catch (Exception e)
            {
                errorMessage = e.ToString();
                return errorMessage;
            }

            try
            {
                Response.Clear();
                Response.Buffer = true;

                Response.ClearHeaders();
                Response.ClearContent();

                Response.AddHeader("content-disposition", "attachment; filename=" + System.IO.Path.GetFileName(file) + "");
                //Set the appropriate ContentType.
                Response.ContentType = "Application/pdf";

                Response.BinaryWrite(buffer);
                Response.End();
            }
            finally
            {
                //System.IO.File.Delete(file);
            }
            return errorMessage;
        }

But it's not working, I don't know why?
Am I missing something?

Rachana