Pdf file content showing junk characters

I have developed an online portal for recruitment where users upload multiple pdf/word/excel files. The files are getting uploaded successfully, but when i try to view the uploaded files, it always display the junk characters as shown below

This is occurring only on production server, In localhost it works fine. Below is the code to open pdf files:

Dim client As New WebClient()

Dim buffer As [Byte]() = client.DownloadData(flpath)

If buffer IsNot Nothing Then

Response.ContentType = ContentType

Response.AddHeader("content-length", buffer.Length.ToString())

Response.AddHeader("content-disposition", "attachment;filename=" & Guid.NewGuid.ToString)

Response.BinaryWrite(buffer)

Response.Flush()

Response.End()

Is it a server isssue ?

Kindly Help on this

Thnaks