Open a PDF file with security

I used code below open a PDF file but got a error said

The specified executable is not a valid application for this OS platform

But, if I open non-security folder as Process.Start(FILE_NAME) will be no problem.

How to fix it?

Dim FILE_NAME As String = "\\MYSERVER\ORDER\N1234.PDF"
Process.Start(FILE_NAME, "USERNAME", ToSecureString("MYPASSWORD"), "DOMAINNAME")